Need to charge the 2 Varta H3 100Ah 12V batteries on the combine see photo. If I charge them in situ without disconnecting the leads am I charging at 12V or 24V? Is it ok to charge them without disconnecting them from the combine? I need to buy a new charger, what electronics protection is best please? The combine is a NH TF78 ELECTRA PLUS, I really don’t won’t to upset the electrics on that.