Neato replacement batteries?

Hi!

I was quite lucky to get a working Neato XV21 in a Fuku a little while back. I do want to keep it going with a fresh battery as it only lasts around 20 minutes these days.

What brand replacement have you guys bought? I have tried to research but it seems any articles written are by folks who are either working for a company or don't know much about batteries, as their suggested battery has terrible reviews.

As a note, I did buy a set of PowerExtra 4000mah batteries and need to return it despite their great reviews. One of them melted through its case after the first use.

The choices left seem to be:
1. OEM $50 3200mah (Seems safest, smallest battery)
2. HQRP ~$50 3800mah (Fairly well reviewed, larger capacity)
3. Synergy ~$40 3500mah (A little less expensive, middling-good reviews)
4. Lithium Power $90 4400mah Li-ion battery (extensive research points to being an expensive gimmick as Neato's NiMH native charger can work with the control board on the battery, but not really realize its capacity)