Updated: Jun 9, 2019
We've spent a few nights here and there without being hooked up to shore power, which means the motorhome's house batteries are supplying the power for lights, refrigerator, freezer, water pump and TV. Even though the furnace is fueled by propane, the fan to blow that hot air is electric.
When we're not plugged in, the standard 1000W inverter takes the 12V from the batteries and makes it into 110V to power most of our stuff, but it's not beefy enough to power the microwave or air conditioning. For that we would need to fire up the generator, which is noisy enough to create a lot of enemies at a campground. Or, we could start up the engine and the alternator will charge the coach batteries and power all the electrical items we want. But idling the Mercedes diesel engine for extended periods can damage the emissions system. And any time you have to visit the Mercedes dealership out of warranty, you might as well sell a kidney.
The coach came with a pair of AGM batteries totaling 160Ah and a single 100W solar panel to help replenish them. That's great for getting by if you're parked at the soccer field for the morning. But if you're camping without being hooked up with an electrical cord, by the time morning rolls around the batteries, which when full are up around 12.7 volts, get down to around 12.1 volts. That's 50% discharged and it's as far as you want to go to avoid degrading the battery innards and shortening their life span.
The previous owner had not been kind to the original batteries. So I replaced the abused batteries with a pair of new larger ones to get 220Ah. Since if you're not supposed to let them discharge more than 50%, that's only 110Ah of usable juice. That's like being served a plate of food and being told you can only eat half of it... every time you eat. That's just not right. Something must be done!
As if a well crafted motorhome wasn't already expensive enough, lots of people add more solar panels and more heavy AGM batteries. Some people upgrade to lithium batteries which have a far greater energy density. They are about 1/3 the weight and about 1/3 the size of deep cycle AGM batteries to get the same number of amp hours. In a small motorhome that's a big deal. That's frees up enough room for a case of your favorite adult beverage.
Another great thing about lithium batteries is they don't mind being discharged a lot more. 80% depth of discharge is the common threshold to adhere to. That's a lot better. We would be saving weight, saving space, and we'd get to eat more of that food on our plate. All we need is a Platinum Visa, cause they're damned expensive. That's the curse of everything manufactured throughout all time; better solutions always cost more.
A full conversion to lithium batteries, with more solar panels and a larger inverter so we can power the microwave, professionally installed, can easily range between $8000 to $20,000. That's not going happen. We don't need to be away from an electrical cord for weeks at a time. We just need to be self sustaining for one to three nights. Surely there's a better solution for our situation and I think a lot of other people are in the same boat. And, by cracky, I think I've found it !