A 3A charger from walmart is pretty good - connect it to the car and let it trickle charge.

However if your battery is really old, there is not much hope - the plates wear out (thats what the mud is in the bottom of an old battery). At best you can wash out an old battery, fill it with new electrolyte and then charge it (at its bubbling voltage - this is dependant on the chemistry of the battery) - then let it rest and retest again.

A small way I have found with my small charger is that if the battery charges too quick - its bad. time to replace it.

and I always look for small businesses or businesses who sell good materials, e.g. there is a shop in my town that is in the battery business for ages and has good ones - in all price ranges and types.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)