Battery choices for Woodstocks

[jupiters_spot]

A number of folks have rebuilt the battery packs for Woodstock calculators (HP21/22/25(c)/27/29C) using commercially available AA-size rechargeable batteries, and I'm embarking on that project for a couple of my calculators.

A question: what batteries seem to be good candidates?

My findings so far:
- not all AA batteries have the same form factor. In fact Wikipedia says: "An AA cell measures 49.2–50.5 mm (1.94–1.99 in) in length, including the button terminal—and 13.5–14.5 mm (0.53–0.57 in) in diameter. The positive terminal button should be a minimum 1 mm high and a maximum 5.5 mm in diameter, the flat negative terminal should be a minimum diameter of 7 mm." In my experience there is a lot of variation in the height of the positive terminal button, which matters as it controls how much of the button protrudes from the plastic battery carrier, which determines how well the battery interfaces with the contact on the calculator's printed circuit board.
- These batteries have positive terminal buttons that are too short for effective use in Woodstocks: La Crosse Tech NiMH 2600 mAh; Sanyo HR-3U 1.2v NiMH
- Sanyo eneloop (HR-3UTG) NiMH are just too long overall; most commercially available springs + this battery = too long to fit in the plastic battery carrier.
- I have had best luck with Amazon Basics AA/HR6 NiMH batteries (vintage 2011, since that's what I had around the house). Nice positive button length, overall length is good.

If you have had good luck with a specific brand/model of AA rechargeable battery, please share your experience.