I do it from time to time. The trick is not to hit it with allot of voltage or risk it blowing up.
Most smart chargers won't charge a battery that is completly dead. Then sense 0 volts and simply won't charge it.
I have a basic Canadian Tire 6/12 volt trickle charger. I charge the battery for about 30 seconds to a minute. Throw on some eye pro and monitor for the battery heating. If it starts geting warm take it off and toss it as it won't take any charge at all and is converting it directly to heat. They have never gotten hot in my experience using this technique.
After that initial short forced charge, the smart charger will read voltage and start charging the battery. I have kick started 5 batteries I found in a drawer that were dead for about 2 years. If it still doesn't charge, toss it. If it does you might have to condition it.. (as you are now noticing)
Last edited by Blackthorne; April 24th, 2012 at 15:19..