Bests & Worsts Reviews from Amazon

Fuvaly 1.5v Lithium AA 4x Rechargeable Batteries Summary Pros: * Lights are helpful * Very lightweight * 1.6v unloaded output voltage is great; 1.55v or higher, consistent and based on load * Stays cool Cons: * Tested when new to 82.5% of stated capacity (1.857 Wh instead of 2.25 Wh), a little low but in the expected range * Almost no warning when out of power. Cannot be used in critical devices where power cannot be lost. * More expensive than 1.2v NiMH Background My intended use for these is for wireless Xbox controllers (2 AA) and wireless Oculus touch controllers (1 AA). I have been using high capacity rechargeable NMHi 1.2v AA batteries for a couple years in the XBox controllers. I've tried two models, a 2800mah kind and 2500 mah turnigy brand, marked as low self-discharge. I tested the capacity of these NmHi batteries which were good, however my xbox never showed a full battery, even when freshly recharged, and it would warn for some time that the battery was low. It was good to get the warning and have more use before having to swap them (days of use), but I felt I never got enough life out of these batteries. The 2500 mah Turnigy brand seemed to last longer than the larger capacity ones because they seemed to hold a high voltage. In the oculus it was the same, where some fresh batteries were immediately detected as low. It is true that alkaline batteries start at 1.5v but quickly drop voltage and spend more of their life at 1.3v and 1.2v, and that is why rechargeables match that voltage, but I wanted to try a battery that sustained a higher voltage and see if they provided more "usable" power. I chose these Fuvaly because they were the ONLY AA Lithium on amazon who posted details such as discharge rates. I saw these are not a good fit for high discharge rate devices such as camera flashes and some toys like RC vehicles. Having an indicator light and a charge port are superior to batteries where one must remove and replace batteries to reset them and there is no indicator that says what the battery is doing (on or off or charging). Capacity Test I performed a discharge test on standard 4 button charger of a single cell using 0.4a discharge rate, which should last two or three hours. I was happy to see the voltage was a high and consistent based on load for the duration of the test. 1.56v for 0.4a. After it shut off, I let it settle a little and tried to get more out but there was nothing left. I got a total 1.857 Wh of energy out. This is 82.5% of the reported 2.25 Wh capacity. Instead of the reported 1500 mah at 1.5v, I got 1238 mah. This is an expected result due to efficiency loss of the step down conversion, and use of cheap components. I did expect a little better efficiency because the battery must have a 3.7v nominal voltage and output requires only a step down (not a boost converter). Also I did not feel any heat during discharge; that means little loss to heat and it is likely the underlying battery capacity less than 2.25 Wh. I did not test the maximum discharge rate. The good news is the unloaded voltage targets 1.6v, not 1.5v; the voltage dips relative to the load and stays consistent. This means under load the voltage is well above 1.5v. Providing power at a high voltage helps with efficiency. When power runs out on a single cell, the voltage drops to about 1.2v for only 10 seconds or so before completely shutting off. This means electronics get almost no warning when they are out of battery, and the battery and the device will shut off with almost no warning compared to 1.2v NmHi rechargeables. This is compounded when using two or more of these in the same device; the device will be shut off when any one battery is drained. Do not use these batteries in critical devices such as a transmitter for radio controlled aircraft; they will shut off without warning. Charges at 0.36a at 5v, or 1.8 Watts. I did not open the cell but I suspect it is a 1S 600mah Lithium ion polymer battery. These typically discharge at 5% a month and have a charge shelf life of 300 days. For the best care, do not leave the batteries at a low state; charge them immediately if drained. For slightly longer life, if you are storing them, they are better stored at 35% to 55% capacity or so (50%), not at a full charge. However if you charge them, they will lose 5% a month so it's a good compromise between being ready and storage voltage. Do not charge lithium batteries unattended; use a fire-safe surface such as granite counter top or cement floor; if they become very hot to the touch during charging or discharging, remove them. Recycle them at batteries plus or other store. I will revise my review after more use in devices. Recommendations: * To those who designed and created this: thank you for sharing detailed specifications. Thank you for the lights and physical design and on off behavior. * More capacity would always be welcomed. * These batteries would be perfect if you changed the circuit programming to provide a longer warning voltage time period when the battery is nearly drained. -- Especially under lower loads, there should be 5 or 10 minutes of warning, say at 1.22v. Under moderate loads, there should be a minimum 2 minute warning low voltage. I would prefer this to be longer so that as the battery ages, and gets worse, the warning system would still be ample. This would make the battery more usable as it ages, even as the capacity shrinks.