Topic among the most delicate: the batteries of the camper in winter . The first thing to say is that both the engine battery and the service battery (or ones) must be in good condition to face the cold which, in itself, will cause a greater discharge.
Obviously, speaking of service battery, knowing the absorption of the on-board utilities that you normally use will help you know your autonomy. As a general rule, the needs should not exceed 30%-40% of the battery capacity. Now I don't want to go into technical formulas and definitions that I wouldn't be able to deal with competently, but I would instead like to talk about how to deal with the first camper outings in cold temperatures in practice and have the opportunity to gain personal experience.
Speaking of parking without connection to the electricity network (connected to the 220 v you will never have problems), the questions to ask are: how much consumption? How much can I recharge the batteries during the day?
Yes, because batteries are basically like a current account, what matters is the balance : the more I spend, the more I have to enter. With one peculiarity: there is no credit line, indeed there is a minimum stock under which I must not go, on pain of battery health or even its damage.
In winter, already in the early afternoon and until the following morning, the batteries will supply the current necessary for life on board, but they will certainly not receive any recharge. To "top up" them we will basically have two possibilities:
through solar panels, but there won't be much time (it's early night) and the panels won't be as efficient as in summer due to the position of the sun, so they may not be able to re-establish the charge used.
through the engine alternator, i.e. by moving, a typical situation of a nice traveling trip. Even here, however, the recharge will be a consequence of the travel time: short distance, short recharge.
I clarify that I have deliberately not taken into consideration other systems for recharging the batteries, Petrol generators (of which I am not an admirer), gas generators, as the argument would be misleading with respect to the objective of this article.
Service battery volts at rest
So the rule : let's not waste electricity and monitor the battery charge at least through the control unit panel. Although imprecise, checking the voltage of the batteries will still give us an indication of what is happening, considering that, at rest and well charged, the voltage of a battery in good condition is approximately 12.8 13.0 volts.This value drops, and it is normal, while the battery supplies current, to return above 12 volts (depending on how much we have absorbed) as soon as we disconnect everything. Already at 12.2 volts (at rest) the battery has been discharged to around 50% and needs recharging, it would be better never to drop it to these levels to avoid shortening its life too much. If recharging it doesn't raise the voltage or the charge is unusually quick to drop back to a low voltage on first use, then I'm sorry, but I think it's time to change the battery. For winter outings (always without connection to the 220) the camper should, if not say must, have two service batteries. I am speaking of the normal gel or AGM batteries normally used, and not of the LiFePO4 which we have been hearing about for some time now.
The starter cables are always useful , correctly sized given the starting point of the engine batteries and the necessary amperage.
It could be useful to buy, without spending much, an amperometric clamp , to easily measure the absorption of the on-board users and to better size the cell battery pack.