I keep all my old car, and boat batteries and use for backups to generator or boosting car, tractor etc. Alternate charging them on trickle charger and they seem to last for 3 or 4 more years of emergency use.
Use them with inverters and they will help power a light or even a tv. Charge them all back up when running generator.

Middle of winter and grass is under three feet of snow, then go grab that lawn tractor battery. Don’t forget the gas in it if needed!
If you do not need the gas, charge the battery from the tractor!
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