I use mock PEQ-15 battery box using this PEQ sized battery (before I switched to deans) as a means to fit a battery. It’s unfortunate that the handguard have very little battery space. Also PTS EPM mags work super well with the MCX if you’re worried about mag compatibility. They are a bit pricey but they are genuinely the best mags on the market ?
I was surprised to discover that a TM MP7 is perfectly capable of holding its own in woodland as well as urban/CQB and they shoot miles with green gas and heavier bb’s.
Get one, you won’t regret it.