Although two batteries are needed would the split relay be enough power to run an electric reel and hot water Heatwave type heater or do I need to charge the batteries.
While some cleaners seem to make it work with a B2B charger (or split charge relay,) most of us just don't do enough mileage to completely recharge our leisure battery.
The other day there were two of us working from my van with the diesel heater going. We used 15 amps of battery charge that day from my leisure battery. My B2B battery charger was recharging my leisure battery at 8 amps on the way home, which was 10 miles away. My battery monitor advised that I had charged my leisure battery by 3 amps by the time I got home.
If I went back to the area I was working in the day before, I might replace another 3 amps, which means I start my day with a deficit of 9 amps from the previous day. Battery recharging isn't straight forward. The fuller a battery gets, the lower the rate of charge it will accept. The lower the state of charge, the higher the charge it will accept. This is the nature of lead acid batteries.
So if my battery is 40 % charged (60% discharged) then my charge rate could be in the region of 8 to 10 amps doing that 10 miles home. But on short journeys (time and distance) you will always need to bench charge your batteries regularly.
I plug mine in every night.
LifePO4 lithium batteries are able to accept a much higher rate of charge. My B2B battery charger is a 60amp unit. And that lithium battery will accept that charge rate. This means that I probably won't need to bench charge that battery. However, winter is another issue, as is price.
Why would I pay £600 for a 100 amp lithium battery when I manage quite well with a 100 amp leisure battery for £100; and I can recharge it when the temperatures are below freezing.