Hey guys, I have two questions. I fly a Firebird Phantom and it came with a variable rate charger which is adjustable from 0.3 to 0.5, for 300 - 500 mah NiMH batteries of 4 to 7 cells. The packs I use are 7 cell, 8.4v, 300mah, for a 180 size motor. The first question I have is, other than the first few charges, is there any advantage or benefit (ie stronger charge, or extended battery life) to be had from charging at 0.3? I've been charging them all at 0.5 and they're warm and "motivated" when I fly them right off the charger, but I think I read somewhere that it's good to charge them on the low rate sometimes. Can anyone verify this? Or call BS if it's not true? Second question. The charger works from a wall adapter or plugs into a cigarette lighter. I use it both ways, but in my truck ('07 GMC Sierra) the charger only seems to work when the engine is running. Seems like maybe it needs a bit over 12 volts to charge. The same outlets power up my cell phone charger and radar detector, with the ignition and engine off. My plane's charger needs not only the ignition on but also the engine running. Is this common? Maybe it's something built in to help prevent the vehicle's battery from being depleted. I'm thinking of using a cheap 12 volt battery and a boat type cigarette lighter outlet to connect directly to charge and/or top off my other packs while I'm flying, so I don't have to burn gas idling my truck to charge. I figure a good full charge on the 12 volt battery should last for probably at least a few weeks, but I'm just guessing, and maybe it won't even work. ANYHOO... I know this is a bit long-winded. Thanks in advance for any advice on these issues.

Generally, you shouldn't charge a battery above 1C. So a 300Mah battery should not be charged above 0.3 amps. It should take just over an hour to fully charge.

Originally Posted by kalnaren

Generally, you shouldn't charge a battery above 1C. So a 300Mah battery should not be charged above 0.3 amps. It should take just over an hour to fully charge.

So does charging at this rate provide a stronger or more thorough charge?

Originally Posted by Stingray8854

So does charging at this rate provide a stronger or more thorough charge?

It provides less chance of damaging the battery. Charging faster will heat the battery up more. Heat will kill batteries. Now, that's not to say they shouldn't be warm. A battery will warm up during charging and probably get warmer during discharge, but it should never be so warm as to be uncomfortable to handle, and it should NEVER be too hot to touch.

Charging at faster than 1C generally produces more heat than is necessary. I don't know if it provides any less thorough of a charge, but it's certainly harder on the battery.