There is a Siglent power supply (don't reacal the exact model) with 4 channels, out of which 2 can act either as a source or as a load, IIRC they are also isolated. DP800 certainly can only source current (so can not act like a load).
I have a DP832 bought about 10 years ago, and was reasonably OK, thought it has some pitfalls. The most annoying for me was the fan, very noisy for a home lab, that's why my DP832 stayed mostly unused. Numerical pad was very useful, indeed, thought the other controls were very cumbersome to use, and with software bugs. Many were fixed with later firmware updates, but it took years, and people still find new bugs here and there, even after 10 years of firmware upgrades. Though, the software support was good for Rigol, in the sense that they are still releasing fixes and upgrades after 10 years, they didn't abandon support.
A normal CV-CC can be used to discharge batteries, but that's more like a hack, cumbersome in practice (
https://www.eevblog.com/forum/projects/cc-cv-power-supply-as-a-contolled-load-for-batteries-(i-e-rigol-dp832)/ ). If I were to buy again, I would chose something that can act as a load, too. IIRC both Rigol900 and Siglent can do that, but please check the specs to be sure that is correct. I'll probably get a Siglent, for heaving more isolated channels, more precise measurement of I/U on the front panel, and for working as a load, too.
For either Rigol or Siglent, they can be unlocked to get all the software upgrades, so you can buy the cheapest model (the hardware is the same for all the models of a given line) then unlock later to full option.
DP832 and DP832A are the same in hardware, but with different software options. I've bought a DP832 and upgraded it later, now it's a DP832A. I wouldn't recommend a DP832 in 2024, if it has to be a Rigol, then get the DP900, though by the specs, Siglent has plenty of extra features.