Anyone else gone down the cheap Chinese MPPT rabbit hole? Here's what I found after 6 months

I picked up a 40A MPPT controller off AliExpress back in January for about £28 — branded "Renogy-compatible" which should've been a red flag, but I was fitting out a small camper on a tight budget and couldn't justify £90+ for a Victron. Paired it with two 100W panels on the roof and a 100Ah leisure battery.

Honestly? For the first three months it was fine. Proper MPPT tracking, hit around 18-19A on a decent sunny afternoon, and the voltage readout seemed accurate when I checked it against my multimeter. I was quietly smug about it. Then around April it started showing battery voltage about 0.4V higher than actual, which meant it was cutting absorption charge short — my battery was sitting at maybe 80% capacity thinking it was full.

I've since recalibrated it using the offset setting buried in the menu (took ages to find any documentation, had to use a translated PDF from a random forum) and it's behaving again. But it got me wondering how many people are running these cheap units without realising their battery's never actually getting a full charge cycle. Over winter that could really hammer a battery.

Has anyone else had similar voltage drift issues, or found a sweet spot brand/price point that's actually reliable without going full Victron? Keen to know what's working for people at the budget end.

@EllaDixon71 oh god the "renogy-compatible" branding 😂 that's doing a lot of heavy lifting isn't it

Had similar on the boat last year - grabbed a no-name 30A off eBay for £22 thinking I was dead clever. Bluetooth app never worked properly, the stated efficiency figures were complete fiction, and after about 4 months it started getting properly hot even on cloudy days. Not warm. Hot.

Ended up just biting the bullet and getting a Victron 75/15 - yes it cost more than my original "bargain" controller but it's been rock solid since.

Lesson learned the hard way: cheap MPPT is false economy when you're protecting expensive lithium cells. What happened with yours after 6 months - still running or did it give up the ghost?