Aldi Activ Energy Smart Charger for AA/AAA NiMH

The last time i used this charger it didn’t shut off (so called Smart) and the cells were almost too hot to touch.

i suppose the high temperature is harmful to the cell lifetime.

Opened it up and found a loose solder joint where the trace was lifted from the board. This was on one of the arms that makes the + contact to one of the 4 cells. There is a 14-pin IC but the marking code has been ground or etched off. i can see it has current sense resistors but no temperature sensing device. More reverse engineering needed.

What is a normal temperature increase that might be expected during charging of AA NiMH cells?

Warm > noticeably warm.
Too hot to hold is TOO hot and damaging.
Very old or poor batteries with high internal resistance may not terminate properly in a good charger.

You SURE you even want that charger? Did a bit of searching and does not sound like a great piece of kit, charger or batteries.
You can get decent basic multi-chemistry chargers inexpensively. You can get good ones for not a whole lot more.

Thanks for confirming my guess—i figured it wasn’t shutting off and trying to overcharge when the cells were not just warm, but hot.

It is a poorly made device with crappy pcb traces. i have other 4x chargers, this is probably not worth trying to repair.

none of the aldi nimh products are worth anything.
cells get 500mohm IR after only 30 cycles.
now IKEA is a completely different story. even their new cheap stenkol charger is good. terminates a bit cooler than my BC700 as it uses 0dV.