Mighty Max Battery 12V 35AH U1 Lithium Battery Replaces Craftsman 25780 Lawn Tractor and Mower

What It Is

The Mighty Max Battery 12V 35AH U1 Lithium Battery is a direct replacement for the Craftsman 25780 and similar lawn tractor batteries. It powers the starter motor and electrical system on riding mowers, zero-turns, and garden tractors with a 12V system. Its lithium chemistry offers lighter weight and longer shelf life than traditional lead-acid batteries.

Fitment & Compatibility

Before buying, verify your machine uses a U1 group size battery (roughly 7.7” L x 5.1” W x 6.1” H). This battery fits Craftsman models like the 25780, 247.288860, and many LT1000/2000 series, but also works on John Deere, Troy-Bilt, and Husqvarna tractors with the same footprint. Check your owner’s manual or existing battery label for “12V” and “U1” specs. Measure your battery tray—if it’s tight, note the lithium battery is slightly shorter than lead-acid, so you may need a foam spacer or adapter shim (often included). The terminal posts are SAE standard (positive post is 3/8” diameter, negative is 5/16”), but verify your cable connectors fit; some older tractors use smaller posts and may need adapters.

Key Things to Buy

• Weight & Handling: At ~8 lbs, it’s about half the weight of a lead-acid battery. Easier to install but may shift in the tray if not secured tightly—use the included foam pad or strap.
• Installation Difficulty: Simple swap—disconnect negative terminal first, then positive, remove hold-down, drop in new battery, reconnect positive then negative. No special tools needed, but a 10mm wrench helps.
• Charging & Maintenance: This is a lithium iron phosphate (LiFePO4) battery. It requires a compatible lithium charger (not a standard lead-acid charger) for long-term storage. It holds charge for months without use, but if you let it drain fully, it may damage the internal BMS.
• Cold Weather Performance: Lithium batteries lose capacity in freezing temps. If you store your mower in an unheated shed below 32°F, expect reduced cranking power until the battery warms up. Not ideal for winter storage without a lithium-compatible maintainer.

Should You Buy It

Buy this if you want a lighter, maintenance-free battery that won’t leak acid or sulfate over winter. It’s best for users with a compatible lithium charger and moderate winter storage conditions. Avoid if you frequently mow in sub-freezing temps or need a drop-in replacement without checking terminal size—lead-acid is simpler for those cases.