I have a friend with a 08 GS and he has the BMW battery charger that is made for the bike. Being an Airhead I'm helping him get his 74 Moto Guzzi back on the road and it needs a new battery. He wants to be able to use the BMW charger he already has. I seem to remember reading some batterys need specific chargers. Are the BMW chargers specific for gel batterys or can they be used on any battery.