I have an EVT 4000 with about 4000 km on it. I stopped using it 2 years ago because my work situation changed and my batteries were failing after about 200 cycles, mostly around 70% DOD. These were 4 GS batteries that came with the scooter. I later added 1 BB battery to get a little more speed and range, according to information found on this forum. It worked wonderfully well. I charged it separately.
I regularly put a charger on those batteries, because I know letting them self discharge will kill them. Now,I just got a new battery charger (for a different purpose) which gives a lot of information. I found out that 1 GS battery is simply completely dead. It's at about 9.2 V and the charger won't have it. The BB is still in perfect shape, and the other 3 GS batteries seem to charge forever. They don't reach their proper end-of-charge voltage. Instead, they stay around 13.9 V. The current goes down to 1.5 A. My understanding of these batteries says that, even though they haven't reached their voltage, they are actually overcharging, and indeed, I feel them getting warm. So they're basically converting water into hydrogen and oxygen and recombining those back into water and heat.
Now, I'm looking for a value-for-money way to get going again, and for that I'd like to know what's up with the batteries that charge forever. I Googled around for failure modes, but didn't find my answer. My new charger has an option to discharge the battery to a voltage level that I can set, in order to see how much capacity is left, but I know this will hurt the battery. The manual recommends going down to 1.7 V per cell to get conclusive information, but if I'd do it, I wouldn't go lower than 2.0 V per cell.
So, does any of you guys know what's up with these 3 GS batteries? Do you think they're still OK?
I'd make 1 change in my way of dealing with them: regularly (not every time) charge each one with a single battery charger! I figure, as long as I do that, and I never go deeper than 70% DOD, everything should be OK. Equalisers shouldn't be necessary then, should they? Do you agree?
Furthermore, we people always want everything, don't we? I would like to have a battery charger that can charge all 5 batteries at once, but controls each one separately, while the series connections remain. I would like it to indicate all 5 charge voltages and currents and Ah charged. I would like to be able to set the charge current in the 4A - 15A range. If I need to the scooter to be ready again quickly, I'll set it high. If not, I'll set it low to preserve battery life. It should work on 230V and be as small as a pack of cigarettes, well, not really, but it would be really nice if it fit in the scooter, which my current charger doesn't.
Be happy to hear your ideas!