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A generator battery size chart answers a plain question: which starting battery fits the generator and turns the engine over on a cold morning. The chart below lines up the figures the makers state for each battery, volts and amp-hours and cold cranking amps and case size, so the match comes from the label rather than a guess. Read the generator manual for the size it calls for, then find that row in the chart.
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Generator battery size chart
Every battery in the chart is a 12V starting battery, and every figure comes from the maker. Amp-hours state how much charge the battery holds, CCA states the current it can deliver to crank an engine in the cold, and the case size states whether it fits the tray. Where a maker states no CCA, the chart says so plainly.
| Battery | Volts | Amp-hours | CCA | Case size |
|---|---|---|---|---|
| Mighty Max Battery YB9A-A | 12V | 9 Ah | 130 CCA | 5.30 x 3.00 x 5.25 inches |
| Mighty Max Battery ML9-12NB, Generac XG8000E replacement | 12V | 9 Ah | Not stated | 5.94 x 2.56 x 3.94 inches |
| Mighty Max Battery ML18-12, Champion Generator 9000 7000 | 12V | 18 Ah | Not stated | 7.17 x 3.03 x 6.57 inches |
| Skyrich HJ01-12-GFP, GENMAX OEM part | 12V | 1.2 Ah, 14.4 Wh | 72 CCA | 2.2 x 4.21 x 3.35 inches |
| Skyrich HJ26-16-GFP, GENMAX OEM part | 12V | 1.6 Ah, 19.2 Wh | 96 CCA | 1.02 x 4.13 x 3.15 inches |
| Mighty Max Battery ML18-12, Troy-Bilt 7000 Watt XP replacement | 12V | 18 Ah | Not stated | 7.12 x 3.00 x 6.50 inches |
Match CCA to the generator
CCA, or cold cranking amps, is the figure that decides whether the starter turns on a cold morning. The Mighty Max Battery YB9A-A lists 130 CCA at 12V and 9 Ah, the Skyrich HJ26-16-GFP (on Amazon) lists 96 CCA at 1.6 Ah and 19.2 Wh, and the Skyrich HJ01-12-GFP (on Amazon) lists 72 CCA at 1.2 Ah and 14.4 Wh. The 18 Ah Mighty Max Battery ML18-12 (on Amazon) listings state no CCA, so match those by amp-hours and case size and check the generator manual for the CCA it calls for.
When the manual names a CCA figure, meet it or pass it. A battery with a lower CCA than the manual calls for may crank slowly in the cold, while a higher CCA in the same case size is a safe match. See how to start a portable generator for the starting routine once the battery is in place.
Match amp-hours and watt-hours
Amp-hours state the charge a battery holds, and watt-hours state the same charge in energy terms. The 18 Ah Mighty Max Battery ML18-12 holds the most charge in the chart, followed by the 9 Ah Mighty Max Battery YB9A-A (on Amazon) and ML9-12NB, while the Skyrich HJ26-16-GFP holds 1.6 Ah at 19.2 Wh and the Skyrich HJ01-12-GFP holds 1.2 Ah at 14.4 Wh. Pick the amp-hours the generator manual calls for, and treat a larger amp-hour figure in the same case size as longer cranking reserve rather than a reason to change the size.
Do not swap a starting battery for a deep cycle battery. A starting battery is built to deliver a short, strong crank, while a deep cycle battery is built for steady draw over a long stretch. See types of deep cycle batteries for how the kinds differ.
Check the case size and terminals
Measure the tray and the hold-down before ordering, and compare the result with the case size in the chart. The Mighty Max Battery YB9A-A measures 5.30 x 3.00 x 5.25 inches, the ML9-12NB measures 5.94 x 2.56 x 3.94 inches, and the ML18-12 measures 7.17 x 3.03 x 6.57 inches in the Champion listing and 7.12 x 3.00 x 6.50 inches in the Troy-Bilt listing. The Skyrich HJ01-12-GFP measures 2.2 x 4.21 x 3.35 inches and the HJ26-16-GFP measures 1.02 x 4.13 x 3.15 inches. A battery that is too tall for the tray or too wide for the hold-down is the wrong battery even when the volts and amp-hours match.
Check the terminals too. The Mighty Max Battery listings use nut and bolt terminals, and the YB9A-A lists positive on the left and negative on the right. Match the terminal layout to the generator cables so the leads reach without strain. See how to charge a generator battery for keeping the battery charged between uses.
Keep the battery ready to crank
All of the Mighty Max Battery listings in the chart are sealed lead acid, or SLA, AGM batteries that the maker states can mount in any position and resist shocks and vibration, with a 1 Year warranty. The Skyrich HJ01-12-GFP and HJ26-16-GFP carry a smart battery management system, or BMS, with overcharge protection and an IP65 dust and water resistance mark, and the maker states cold starts as low as -40°F and -20°C. The Skyrich batteries weigh 1/3 of a lead-acid battery and take 1/5 of the space, by the maker, and each carries a 1 Year warranty.
Note that the Skyrich HJ01-12-GFP and HJ26-16-GFP are GENMAX OEM parts made for generator starting only, and the maker states they are not for powersports or motorcycles. A fuel generator runs outdoors only, far from doors and windows, because of carbon monoxide. For safe handling around any generator, see portable generator safety tips.
FAQ: power away from the grid
What size battery does a generator need?
Match the volts, amp-hours and CCA the generator manual calls for, then match the case size to the tray. The chart above covers 12V starting batteries from 1.2 Ah at 72 CCA to 18 Ah, so find the row that matches the manual and the tray.
Can a 9 Ah battery start a generator?
Yes, when the manual calls for it. The Mighty Max Battery YB9A-A lists 12V, 9 Ah and 130 CCA, and the ML9-12NB lists 12V and 9 Ah as a replacement for the Generac XG8000E. Check the manual for the CCA figure before ordering.
What does CCA mean on a generator battery?
CCA stands for cold cranking amps, the current a battery can deliver to crank an engine in the cold. A higher CCA in the same case size gives more cranking strength, and the manual states the figure the generator needs.
Are generator starting batteries the same as deep cycle batteries?
No. A starting battery delivers a short, strong crank to start an engine, while a deep cycle battery gives steady draw over a long stretch. The Skyrich starting batteries in the chart are made for generator starting only, and the maker states they are not for powersports or motorcycles.
Related solar guides
See every batteries guide, plus how to charge a generator battery, what is a battery management system and how to start a portable generator.
