Leaderboard

Huge batteries like those ones should be charged with a 10 amp or larger charger. Trickle chargers are only good for keeping one already fully charged topped up, and even then some require the larger trickle chargers because of internal leakage not noticeable on smaller batteries. You can "shock" those big batteries into taking a charge sometimes by hitting them with 24 or more volts DC. Connect two 12v batteries in series and then connecting to the terminals on the big dead one for a few seconds. It may knock a little sulphate off the cells and allow them to show enough voltage your trickle charger or bigger electronic charger will start up on it . Only hit the dead battery for a few seconds at a time and be sure to be where any acid that might boil out won't hurt anything..especially you. The best way to try to get them to take a charge though is with one of the old chargers that were basically just a transformer and rectifier. They don't sense the battery voltage, They just supply a constant voltage that at first will show nearly no charge rate until the battery has gained a little voltage back. As battery voltage rises the charge increases but when it is near the charge output voltage the rate drops again. Those old chargers don't shut off when the battery reaches full charged voltage . They will keep pumping current into the battery until it boils out or shorts. It's worth a try if you have the batteries there .. You may get lucky. Otherwise hopefully you have a recycler there that will pay you for their lead content. I took about a half dozen dead batteries of various sizes to a recycler here and walked out with over $100 in my pocket

Some of the maintainers come with that connector so you have a quick way to attach the charger. No harm in attaching it. The only way it could have damaged the battery is if it overcharged it for a long time. (as in the charger is defective) you can check that by measuring the voltage on the battery with the charger attached. It should not exceed 14.5 volts. For a charger to "boil" out your battery, you would see over 17 volts. Mike