Please critique my electrics plan!

I am about to purchase an already converted van but at the moment it has no leisure battery. It has a 12v electric cooler but everything else the current owner has been using has been battery operated. I am about to live pretty much full time in the van from October through to March in the UK and I think I am going to need a battery. The current owner of the van says he ‘plugs (the cooler) into cigarette socket and solar trickle charger for van battery but I’ve had it on for 24 hours and doesn’t use anything, van still started’. I don’t know the specifications for the cooler but this seems precarious to me?!

As living full time in the van, I will need to charge my laptop (45w) for around 2 hours a day, charge my mobile phone and a few LED lights. I will shower at work, and once a week I will stay with family where I can freeze a big bottle of water to put in the cooler so won’t need it on at least for a few days (I hope!) I am thinking about installing a diesel heater if the supplied gas heater doesn’t do a good job. Anything I’m missing?

I am planning on getting a 300w inverter to charge my laptop, a 100ah AGM battery, and a 30A B2B charger. My head is fried from trying to do all the maths and I have got myself all confused. Would this system work for me? If I drive an hour a day, that will add 30ah back onto my leisure battery right?

Please, any tips or insight would be so appreciated!

Here’s a tutorial I wrote on installing solar. It applies to any way you wish to do it, even without solar.

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Thank you, that was so helpful! I had never even thought about a laptop car charger before, amazing to be able to scrap the inverter. Using the advice in your tutorial I have figured out that I need a total of 45ah per day. If I follow your advice of having 2 days worth free before needing to charge then I would need a 180ah battery. I am not convinced this is necessary in my instance as my battery will be charged by my starter engine not solar, I will never be stationary for more than 12 hours at a time. Now I just need to figure out how much I would need to drive per day to recharge those 45ah! Any ideas?

Edit: I have just realised that the B2B charger is for newer vehicles that have the stop/start engines. I think I need to look at split charge instead.

You’ll have to figure out how much excess power your alternator produces while the vehicle is running. Alternators typically produce enough to run the vehicle electronics (ignition, ECU, lights, sensors, etc), plus some excess. Find that excess and you’ll have the answer. Be sure to account for losses through the battery isolator and wiring.

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Also, since you’re not using a charge controller, install a low voltage cutoff device between the battery and fuse panel. This will prevent battery-damaging over-discharge.

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