Someone asked exactly this on a UK money and consumer forum recently, in a thread about housing a battery and inverter outdoors. Pressure-treated timber, a rubber roof on top, built to brave the elements. Their own words: "i reckon it should be ok as long as its pressure treated... Any thoughts if this is viable?" It's a reasonable question, and it's one a lot of people are quietly asking themselves before they order anything.
The replies are worth reading in full, because between them they cover almost everything that actually goes wrong.
"Would a wood structure even be strong enough?"
That was their own follow-up question, and it's the first snag in the plan. A battery and inverter together aren't small, and a timber box strong enough to carry that protection, season after season, outdoors, is a bigger build than "pressure-treated and a rubber roof" suggests. Strength has to survive years of freeze-thaw and damp timber, not just the day it's built.
"The battery can be permanently damaged if the cells freeze"
This is the one that should stop anyone in their tracks. One reply laid out the real mechanism: charging throttles once the battery drops below 5°C, and if the cells actually freeze, the damage doesn't reverse. That's not a performance dip you can wait out, it's permanent. A DIY box with no thought given to that threshold is gambling with the one component that's actually expensive to replace.
"Make sure that any insulation can be removed in the summer, and that there will be adequate ventilation"
The advice that came back wasn't "add insulation and you're sorted." It was a warning that insulation without a way to shed heat in summer just trades one failure mode for another. Solving cold and solving heat are two different engineering problems, and a single sealed box rarely solves both at once. That's not a skill issue, it's a design one, and it's exactly why manufacturer guidance treats them as separate requirements rather than one blanket "add a cover" instruction.
"The installation manual does suggest a cover of some kind"
This isn't a stranger's opinion on a forum, either. It's straight from the manufacturer's own installation guidance, cover or shade, one or the other, non-negotiable. A homemade box either meets that bar or it doesn't, and there's no manual to check the build against once it's up.
"Are you confident a wooden box in the front yard will be safe from thieves?"
The last reply raised something nobody in the thread had mentioned yet. A visibly homemade enclosure, sitting in a front garden, reads differently to an opportunist than a proper, finished unit does. Not the main reason to think twice, but a real one, and one that costs nothing to consider before the first cut of timber.
What this one thread actually proves
Nobody in that conversation said the idea was mad. They said it needed to survive freezing, manage two opposite heat problems at once, hold real weight for years, match what the manufacturer's manual actually requires, and not look like an easy target sitting out front. That's not a weekend build, that's a spec sheet. Worth knowing before the first sheet of ply is cut, not after.
Source: real forum discussion, Outdoor Housing for Battery and Inverter, MoneySavingExpert Forum