Anyone else finding cheap MPPT controllers a false economy? My Renogy 40A experience

Been running a Renogy Wanderer 40A MPPT on my shed setup for about 18 months now — two 200W panels going into a 200Ah lithium leisure battery. On paper it all looked fine, but I've been noticing the charge figures just don't add up. Decent sunny day, panels putting out around 28V open circuit, and I'm lucky to see 15A going into the battery. Something's clearly getting lost somewhere.

Had a proper look at the wiring, checked connections, even swapped out the cable run thinking it might be voltage drop. No real difference. Started logging the data through the Bluetooth app and the efficiency figures it's reporting look optimistic to me — claiming 97%+ conversion but the actual amp-hours landing in the battery tell a different story when I cross-reference with my Victron BMV-712 shunt.

Wondering if anyone else has had similar with the budget MPPT units? I'm half-tempted to just bite the bullet and get a Victron SmartSolar 100/30 — the price difference hurts but if it's actually harvesting what my panels can produce it'll pay back eventually. Has anyone done a direct swap like this and noticed a measurable improvement, or am I just chasing ghosts here?

Swapped out a knock-off MPPT for a Victron 100/30 in my van last year and honestly it paid for itself in recovered charge cycles before I'd even finished the second brew. 🍵

@ColJames74 the absorption/float transition on cheaper controllers is often where it falls apart with lithium — they'll either cut off too early or keep topping up when they shouldn't. Worth logging what your actual charge profile looks like if you can; a basic Bluetooth shunt (I use a Victron BMV-712) will show you pretty quickly whether you're actually getting the amp-hours you think you are.

Had similar suspicions about a Renogy unit on my EV charging setup — the panel harvest looked plausible on paper but the car was consistently getting less than expected. Swapped to a Victron SmartSolar 100/30 and suddenly everything made sense in VictronConnect. The MPPT algorithm alone recovered probably 10-15% more on overcast days.

Sometimes the controller is quietly losing you more than a bigger panel array would gain you.

Really resonates with this one. Had a "budget" MPPT on my first motorhome build — wouldn't properly communicate with the battery BMS and I was essentially flying blind for months. Switched to a Victron SmartSolar 100/20 and the Bluetooth visibility alone changed everything. You can actually see what's happening in the app, catch problems early.

@Shunt_Geek makes a fair point about the absorption/float issue — on my tiny house setup I run Fogstar Drift lithium cells and the charge profile precision genuinely matters for longevity.

The maths usually works out: a Victron costs maybe £40–60 more upfront, but if it's wringing an extra 10–15% efficiency from your panels and not quietly cooking your expensive lithium bank... it's not even a close decision over a 5-year horizon.