Here a response from Trojan regarding charging current, 10-20% C20
'Below is Trojan Battery's response:
There is really no limit to how high the initial charge current can be. We recommend that range of charge currents because charge systems are usually power limited and so we have to give customers a range. There are two things that you have to watch for when using high currents to charge batteries. The first one is that the current must be lowered before the batteries reach a voltage of 2.35 volts-per-cell. The second one is that the battery does not exceed 114°F. The only real advantage of having high charge currents is shorter charge times, but the implementation costs are usually too high.'