After trying several different types of batteries in my Odyssey+ controllers, including alkaline, Ni-MH and single-use lithium batteries, I'm pretty sure that these controllers were originally designed for a single cell Li-ion pack, but some num-nut bean-counter decided to switch it to AA use without thoroughly vetting the change, or they intended to sell a Li-ion add-on pack that never made it to market!

A Li-ion pack would give a top voltage of 4.2v when fully charged, a working voltage of ~3.85v (where most of the battery life is), and a low voltage of, depending on the pack, 3.3v down to 2.7v. And this seems to correspond to the readings on the SteamVR's battery meter as well!

Given that the working voltage of Ni-MH rechargeables is 2.4v (1.2v per cell), it's not surprising that more often than not they simply don't work in these controllers and show as low battery or even dead. And for alkaline, they top at ~3v (~1.5v per cell) and working is ~2.6v (~1.3v per cell), so they always show as nearly dead on the SteamVR's battery meter. Even the single-use lithiums at 1.8v per cell new (2x = 3.6v) show as halfway or so on the battery meter, but last longer than a few play sessions, unlike the alkalines which die pretty fast in the controllers (though there's a lot of life still left in the batteries).

I had been using single-use lithium batteries in my Odyssey+ controllers and when it came time to change them I did some research first. I came across a suggestion made in the Steam forums to use a 14500 Li-ion cell (removed from a solar light) along with a dummy battery. I found the 14500 Li-ion cell to be a really great idea, as this best represents what the controller is designed for, IMHO. And not only that, the 14500 Li-ion batteries are relatively inexpensive and are rechargeable with an inexpensive charger.

So seeing that others have the same problems that I had with the various types of batteries, I picked up a 20x pack of HyperPS dummy AA batteries for around US$9.00 shipped from eBay, and 2x Trustfire 14500 900mAH (2-pack) batteries from www.thecustomsabershop.com for around US$16.90 shipped (4x total batteries, best price I found for reliable Li-ion 14500 batteries with a protection circuit). These two combined still costs the same or less than one set of 1.5V AA Lithium USB rechargeable batteries (even if you throw in a charger, which I didn't need as I have an excellent Xtar VC4 already) and will actually work in the controllers the way they were designed, with a 3.7v Li-ion battery.

The SteamVR battery meter now reads properly and shows full when a fully charged battery is put in the controller, as it should. And this also gives me 2x extra batteries I can swap in when I need them, or I can use Li-ion batteries on other devices capable of handing the increased voltage, such as flashlights and such. So while you could use a Li-ion battery taken from a solar light (as had been suggested) and it would work well, I opted to go with a protected cell to ensure my Odyssey+ controllers wouldn't get damaged by the use of lithium batteries. As well, though you could easy make your own dummy battery (aluminum or copper foil on a dowel rod the size of an AA cell) I bought several sets of dummies as I feel over time I can make use of them and they were cheap enough.

There are a LOT of bad 14500 Li-ion batteries being sold these days, so here's a few things to watch out for:

1. Due to the limitations of the Li-ion chemistry there is a limit to the capacity of a 14500 sized Li-ion battery. Any 14500 sized Li-ion battery rated above 1200mAh is fake, period... And even that 1200mAh rating is fake as in actual use the mAh is closer to 900mAh, they get the higher rating by using a very low discharge rate while testing (the truth of the battery's true capacity, or the lie as it were, is all in the details).

2. As the physics of the current state of the Li-ion technology would dictate, that means legitimate 14500 Li-ion batteries will be in the 600mAh to 900mAh range (given the notable exception in #1 above). They also tend to last through 500 or so recharge cycles (some higher and some lower), making them significantly cheaper than buying disposable batteries in most cases despite the higher initial cost.

3. In my personal experience, fake 14500 sized batteries (rated above 1200mAh) will only have about 250mAh to 500mAh capacity with a severely curtailed number of times it can be recharged. So they seem to work fine at first, but you find yourself recharging and replacing them more often (usually dumping out at JUST the wrong time in a game, LOL). Just spend the money on the real thing instead of wasting money trying to be stingy!

4. Don't forget to pick up a charger for your Li-ion batteries. They make a nice USB charger that uses magnets to attach to the battery and is simple and easy to use, as well as being fairly inexpensive. They also make cheap single cell wall plug chargers, or more expensive smart chargers that take more than one cell at a time (such as my Xtar VC4, that also does NiCad and Ni-MH as well as lithium cells in several different sizes).

5. Get Li-ion 14500 batteries with a built-in protection circuit! While you need not be worried about overcharging if you're using a proper Li-ion charger, you need to worry about over-discharging the battery while it's in the controller. Lithium batteries have a lower limit of discharge, and over-discharging them can ruin them permanently and can be dangerous as well. The built-in protection circuit will simply cut-off discharge before you reach that critical threshold where the battery would be damaged, saving both the battery and the controller in the process.

Using 1.5V AA Lithium USB rechargeable batteries is a viable alternative despite being around twice the cost (if you buy quality batteries), and might be desirable for many people.

1. A 1.5V AA Lithium USB rechargeable battery internally contains a 3.7v lithium cell, so it has nominally 3330 watts of power (watts = 3.7v x 900mAh), so discharging at 1.5v it can supply a nominal 2220mAh of current, and rivals the Ni-MH in terms of capacity. (Note - due to inefficiencies when converting the voltage to 1.5v the total mAh may be a little lower than the calculated amount, but still rivals Ni-MH at around 2000mAh+).

2. These batteries have the advantage that they can keep the voltage constant over the range of the battery's use, so will supply the voltage of ~1.5v until right before the battery goes dead. This means that through the usable life of the batteries, using two of them will provide ~3v until almost depleted. And the WMR controllers seem to be happy with 3v, and though it shows the battery at the low end in SteamVr's battery meter it's still above the critical level and no warnings are triggered until the batteries need to be recharged.

3. The USB charging circuit simplifies the recharging process and also acts as a protection circuit that protects the battery and your controller as well.

4. This means that using a set of two 1.5V AA Lithium USB rechargeable batteries gives you just a little more than twice the capacity of using a single 14500 Li-ion battery with a dummy. This means roughly twice the use before needing to be recharged, an important consideration if you're a heavy gamer!

5. The 'Caveats...' section of this Guide still applies, buy quality batteries and be careful about ratings higher than what the technology can actually support! Crap batteries will kind of work, but not well and not for long...

I switched over to a Quest 2 headset a while ago and the Quest controllers use a single AA battery. So, when I moved over, I had to find a good quality 1.5v AA rechargeable lithium battery for these controllers.

After trying several brands of AA batteries, I found that most fell within that 'crap battery' category I described in the 'Caveats...' section above!

But I did strike gold with the "EBL AA Lithium Batteries, 1.5V 3000mWh Rechargeable" I found on Amazon. These are their red lithium batteries (the EBL black lithium batteries are single use, so you want the red rechargeables).

This means that these EBL AA's would be well suited for using in the WMR controllers as well, though you'd be using 2 per controller rather than 1 as in the Quest.

They need a certain type of charger so buy the bundle that includes one, though I was able to re-use a Deleepow charger I already had with the EBL batteries (Deleepow batteries turned out to be crap batteries just like the rest after a few uses despite looking good initially, the charger was fairly decent though and works well to charge the EBL batteries).

The EBL AA rechargeables batteries maintain most of their charge even when not being used, which means even if you haven't used your headset in a while the batteries in the controller will be ready to go when you are. And they maintain an output of 1.5v until they are ready to die, when the voltage falls off a cliff, so keep that in mind (most if not all rechargeable lithium 1.5v batteries do this so it's normal).

I actually use these EBL rechargeables for other things as well, such as for karaoke mics, electronic mouse traps that like the constant 1.5v, and various other things around the house. My oldest set of EBL batteries are over a year old and have been recharged quite a few times.

I need to add a caveat though, I did have to return one set of EBL batteries for replacement (out of 6 sets I've purchased, though) as one of the batteries in the set failed way before the others and was bad. This can happen to any brand of battery; the question is how prevalent the problem is. On the Deleepow branded batteries, they worked fine 2 or 3 times and then started failing early one at a time until all had the problem. The bad EBL I returned was an outlier but it was there, so you need to be aware this can happen. Just find it early and replace it under the seller's exchange policy or under warranty!

I'm sure there are other quality brands of 1.5v lithium rechargeable AA batteries around, but I wanted to share what I discovered when I fell down that rabbit hole myself. I'm real happy with the EBL batteries as they deliver on their promise of reliable power over a reasonable amount of usage. I use the Deleepow as an example of what to avoid as they are crap batteries and lose their charge fairly swiftly when not used. They seem to work at first and it only becomes obvious they're crap when it's too late to do anything about it! But at least I was able to salvage some decent chargers out of it...