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The battery isolator vs solenoid question comes down to how the second battery connects: an isolator manages charging automatically, while a solenoid is a heavy-duty switch. We compared two isolators and two solenoids by current rating, build, value, safety and warranty, using only what each listing publishes.
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Quick picks
Best Overall KeyLine 140A VSR: A 140A voltage sensitive relay kit that connects at 13.3V and disconnects at 12.8V, with full wiring kit included. Check price on Amazon
Runner-Up STINGER SGP32: A 200A continuous isolator relay with 500A surge capacity and 100,000 mechanical cycle life. Check price on Amazon
Also Great ADsunves Latching Relay: A 100A latching solenoid relay that draws power only when switching, with fuses and hardware included. Check price on Amazon
The picks
| # | Product | Solar Score | Buy |
|---|---|---|---|
| 1 | KeyLine 140A VSR | 9.8/10 | Buy on Amazon |
| 2 | STINGER SGP32 | 9.7/10 | Buy on Amazon |
| 3 | ADsunves Latching Relay | 9.7/10 | Buy on Amazon |
| 4 |  MaySpare Solenoid | 9.6/10 | Buy on Amazon |
KeyLine 140A VSR
A 140A voltage sensitive relay kit that connects at 13.3V and disconnects at 12.8V, with full wiring kit included.
Pros
- Auto VSR: connects at 13.3V, disconnects at 12.8V.
- IP65-rated solid-state design for marine and off-road.
- Complete kit: 20-ft red cable, terminals, lugs, instructions.
- 12-month warranty.
Cons
- 140A is less than the 200A picks.
- 2.6 in. cube needs mounting space.
- No surge rating stated.
- Kit has many small parts to keep track of.
Detailed Review
The KeyLine Iso-Pro140DBK is the set-and-forget isolator: a voltage sensitive relay that automatically connects the auxiliary battery at 13.3V and disconnects at 12.8V, so the starting battery stays charged. Unlike diode isolators, it adds no voltage drop.
The IP65-rated solid-state build suits marine, RV and off-road use, and the kit includes a 20-ft red power cable, 2-ft ground cable, brass terminals, tinned copper lugs and heat shrink. A 12-month warranty is stated.
Its Solar Score of 9.8/10 comes from performance 32/35, build 24/25, value 22/25, safety 8/10 and warranty 3/5: 89 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Current | 140A |
|---|---|
| Rating | IP65 |
| Warranty | 12-month |
Figures as published on the retailer listing, collected 22 October 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. IP65-rated for water, dust and vibration, so safety scores 8 of 10. 12-month warranty. It does not say everything a buyer needs, such as who pays return shipping, so warranty scores 3 of 5. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
STINGER SGP32
A 200A continuous isolator relay with 500A surge capacity and 100,000 mechanical cycle life.
Pros
- 200A continuous, 500A surge capacity.
- 100,000 mechanical cycle life.
- Water-resistant phenolic build for marine and powersports.
- 1 year warranty.
Cons
- No auto voltage sensing; relay operation.
- 1.4 lb is heavy for the size.
- No wiring kit included.
- 12V only.
Detailed Review
The Stinger SGP32 is the high-current isolator: 200A continuous with 500A surges for big car audio systems and accessories. The phenolic plastic construction resists moisture for marine and powersports installs.
A 100,000 mechanical cycle life backs the durability claim, and it works with any 12V alternator or charging system. A 1 year warranty is stated.
Its Solar Score of 9.7/10 comes from performance 33/35, build 22/25, value 21/25, safety 7/10 and warranty 3/5: 86 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Current | 200A |
|---|---|
| Surge | 500A |
| Warranty | 1 year |
Figures as published on the retailer listing, collected 22 October 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. Water-resistant phenolic construction is stated, so safety scores 7 of 10. 1 year. It does not say everything a buyer needs, such as who pays return shipping, so warranty scores 3 of 5. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
ADsunves Latching Relay
A 100A latching solenoid relay that draws power only when switching, with fuses and hardware included.
Pros
- Latching design uses power only on state change.
- 100A rating, -40 to +85C operating range.
- Includes 2 blade fuses, K-nuts, nuts and washers.
- 1-year warranty.
Cons
- 100A is the lowest here.
- Manual operation mode.
- Wiring needs care to avoid shorts.
- Nickel contacts, not copper.
Detailed Review
The ADsunves 0100055000 is a latching battery disconnect solenoid: it holds its state without continuous coil power, drawing current only during switching. That suits RV battery isolation where the relay sits for weeks.
It is rated 100A at 12V with 9V minimum actuation, -40 to +85C operation and 20,000 cycles at full load. The kit includes 2 blade fuses and mounting hardware, and a 1-year warranty is stated.
Its Solar Score of 9.7/10 comes from performance 29/35, build 22/25, value 21/25, safety 7/10 and warranty 3/5: 82 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Current | 100A |
|---|---|
| Temp | -40 to +85C |
| Warranty | 1-year |
Figures as published on the retailer listing, collected 22 October 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. -40 to +85C operating range is stated, so safety scores 7 of 10. 1-year. It does not say everything a buyer needs, such as who pays return shipping, so warranty scores 3 of 5. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
MaySpare Solenoid
A 200A max transient solenoid with 100A rated current and sealed steel case.
Pros
- 200A max transient, 100A rated current.
- Sealed steel case resists corrosion.
- 180C copper coil.
- 3-terminal, normally open.
Cons
- No warranty term stated.
- 150A for 5 minutes only, then needs a break.
- Starter-duty design, not continuous.
- No kit or hardware stated.
Detailed Review
The MaySpare solenoid is a heavy-duty 12V relay: 200A max transient with 100A rated current, in a sealed plated steel case. The 180C copper coil and flat mounting bracket suit winch and marine battery isolation.
Note the duty limit: 150A for 5 minutes needs a cooling break, or it overheats. It is a starter-duty solenoid. No warranty term is stated.
Its Solar Score of 9.6/10 comes from performance 30/35, build 21/25, value 21/25, safety 7/10 and warranty 0/5: 79 of 100 points, placed on our 9.2 to 9.8 scale.
Key Specifications
| Current | 200A max |
|---|---|
| Rated | 100A |
Figures as published on the retailer listing, collected 22 October 2026. Performance figures are manufacturer rated.
Safety and Warranty
What this listing states. Sealed steel case is stated, so safety scores 7 of 10. No warranty term, so warranty scores zero. See How We Pick.
Follow the manual. Connect and use the product as the maker describes, stay within every stated rating, and read the manual before first use.
This is general buying information, not professional advice. Follow each product manual and local rules, and see our Safety Disclaimer.
As an Amazon Associate I earn from qualifying purchases.
Compare the picks
| Pick | Solar Score | Amps | Type | Voltage | Warranty | Amazon |
|---|---|---|---|---|---|---|
| KeyLine 140A VSR | 9.8/10 | 140A | Isolator | 12V | 12-month | View on Amazon |
| STINGER SGP32 | 9.7/10 | 200A | Isolator | 12V | 1 year | View on Amazon |
| ADsunves Latching Relay | 9.7/10 | 100A | Solenoid | 12V | 1 year | View on Amazon |
| MaySpare Solenoid | 9.6/10 | 200A max | Solenoid | 12V | Not stated | View on Amazon |
Specifications are manufacturer rated as listed, collected 22 October 2026. Three of the four picks state a warranty term.
How we scored them
The Solar Score weighs performance, build, value, safety and warranty. For isolators and solenoids, safety means the stated environmental ratings, sealed construction and operating ranges. Three of the four picks state a warranty term. How we pick explains the weights.
| Product | Solar Score | Perf. /35 | Build /25 | Value /25 | Safety /10 | Warranty /5 |
|---|---|---|---|---|---|---|
| KeyLine 140A VSR | 9.8 | 32 | 24 | 22 | 8 | 3 |
| STINGER SGP32 | 9.7 | 33 | 22 | 21 | 7 | 3 |
| ADsunves Latching Relay | 9.7 | 29 | 22 | 21 | 7 | 3 |
| MaySpare Solenoid | 9.6 | 30 | 21 | 21 | 7 | 0 |
Scores run from 9.2 to 9.8: each product’s point total is placed on that range, so more points always means a higher score.
How to choose the best battery isolator vs solenoid
Isolator for automatic charging, solenoid for switching
The KeyLine VSR connects the auxiliary battery at 13.3V and disconnects at 12.8V with no action needed, ideal for dual-battery RV and marine setups. The Stinger SGP32 is a 200A isolator relay for high-draw audio systems. The ADsunves latching solenoid holds its state drawing power only when switching, and the MaySpare is a starter-duty solenoid for intermittent high current. Pick the isolator for charging management and the solenoid for disconnect duty.
| Pick | Current | Warranty |
|---|---|---|
| KeyLine 140A VSR | 140A | 12-month |
| STINGER SGP32 | 200A | 1 year |
| ADsunves Latching | 100A | 1-year |
| MaySpare Solenoid | 200A max | Not stated |
Match amperage to the load
Current ratings here run 100A to 200A continuous, with the Stinger and MaySpare reaching 200A. Size the isolator or solenoid above the maximum sustained draw: the KeyLine 140A suits moderate auxiliary loads, while the Stinger 200A with 500A surge suits big inverters. For inverter sizing, see the pure sine wave vs modified sine wave inverter. The MaySpare handles 150A for 5 minutes only, then needs a cooling break.
Check the environment rating
Engine bays and boats are wet and shaky. The KeyLine is IP65-rated for water, dust and vibration with a solid-state design. The Stinger uses water-resistant phenolic plastic for marine and powersports. The MaySpare has a sealed steel case against corrosion. For 12V system basics, see LiFePO4 battery guides.
Read the warranty and duty cycle
The KeyLine states a 12-month warranty, the Stinger and ADsunves state 1 year, and the MaySpare states no warranty term. Duty matters too: the ADsunves latching relay is rated 20,000 cycles at full load, the Stinger 100,000 mechanical cycles, while the MaySpare is starter-duty with a 5-minute limit at 150A. For the battery itself, see the best 12V battery for teardrop trailer.
Sizing Notes
- Match the isolator amperage to the alternator output and the auxiliary load combined.
- All four picks are 12V; confirm the system voltage before buying.
- Size wiring to the current rating; the KeyLine kit includes 20-ft red and 2-ft black cables.
- Respect duty limits: the MaySpare needs a cooling break after 5 minutes at 150A.
Frequently Asked Questions
What is the difference between a battery isolator and a solenoid?
An isolator like the KeyLine VSR automatically manages charging between two batteries at set voltages. A solenoid like the MaySpare or ADsunves is a heavy-duty relay switch for connecting or disconnecting a battery.
Which pick handles the most current?
The Stinger SGP32 at 200A continuous with 500A surges, and the MaySpare at 200A max transient. The KeyLine is 140A and the ADsunves 100A.
Can a solenoid stay engaged continuously?
The ADsunves latching relay holds state without continuous power. The MaySpare is starter-duty: 150A for 5 minutes needs a cooling break.
Which picks state a warranty?
The KeyLine (12-month), Stinger (1 year) and ADsunves (1-year). The MaySpare states no warranty term.
Are these 12V units?
All four are 12V. The KeyLine activates at 13.3V and disengages at 12.8V; the ADsunves needs 9V minimum to actuate.
Related guides
See every Deep Cycle and RV Batteries guide and all Batteries and Charging guides.
More picks: deep cycle and RV batteries, pure sine wave vs modified sine wave inverters and LiFePO4 batteries.
