Have elite 800x headphones. Get a message after 20 minutes of use to recharge although I charged all night. Do I need a new battery or do some sort of reset? About 3 years old.

The Bluetooth 371 headphones are manufactured by the brand MPOW. According to the manufacturer's website, the headphones use a built-in rechargeable lithium-ion battery, which can be charged using the included micro USB cable. The battery provides up to 20 hours of playtime on a single charge, and can be fully charged in approximately 2.5 hours.
Therefore, the Bluetooth 371 headphones do not require replaceable batteries, as the battery is built into the headphones and can be recharged using the provided micro USB cable.
If you need a quality Bluetooth headphone that has a long lasting battery, do check out the following below;

bestbuy.7tiv.net/Gjr6Bk
https://amzn.to/3IBCFjH

More than likely the rechargeable internal battery has leaked electrolyte, reducing the Ah ("Amp-hour") capacity.
Try to remove the cover to see if battery is leaking, looking like crusty dry salt.
Even if not leaking, the rechargeable cells have a limited lifespan.
If battery, this needs renewal of same V and Ah.

Since it's brand new, return it. You didn't say what type of tablet it is, but they should last for many hours on a charge.

Hi,
It could be that you have damaged the on/off button.
It could be that you have damaged the USB charging port.
OR
Lithium ION batteries are usually rechargeable. The use mode for these batteries is that there are a set number of recharges that equate to the life of the battery. Usually that life is approximately 1,000 charges.
If you use your battery to 50% then recharge, you can do this ~2,000 times. As the life of the battery is used up, the maximum charge lessens which means where you may have had 8 hours of play time when the battery was new, you will only have 6 hours as the battery life is used up.
In order for a Lithium ION battery to recharge there must be at least a small amount of charge left as a "seed" for that recharge. If you drain a L-ION battery down to zero, it may never recharge again or the max charge will be reduced to an insignificant amount of the original full charge. eg instead of 8 hours you may only get 15 minutes, or 5 minutes, or no minutes.
You are much better off recharging when 50% depleted than using it up til your product stops.
L-ION batteries cannot be repaired only replaced. Most cheap products using L-ION batteries cannot have their batteries replaced.

Either the batteries are used up an cannot be charged any longer or the charger is broken.

Hello everyone I phoned olympus on 08001114888 and they said to go into Settings then 'battery type' and chose either alkaline (normal) or NiMH for rechargeable - problem solved!! Not in instructions!!! Previously could only take about 6 photos without 'battery empty' message or the lens going in and out as above. This SHOULD sort out your problems so you can keep the camara :)

BATTERY INSTALLATION AND INFORMATION
Your wireless headphone unit requires two rechargeable AAA batteries.
Rechargeable batteries are uncharged when you purchase them. Before
you can use the wireless headphones, the batteries must be charged for
16 hours. Follow these steps to install and charge the batteries.
Installing the Rechargeable Batteries
Take care to follow these steps to correctly install the batteries.
1. On the right headphone, locate the battery compartment (1).
Use the finger depression on the compartment to turn the battery
compartment cover counterclockwise to remove the cover.
2. Insert two AAA rechargeable batteries, carefully following the
markings inside to ensure the batteries are inserted properly, with
the + and - ends in the correct positions.
3. Replace the battery compartment cover.
Charging the Rechargeable Batteries
To recharge the headset unit, follow the directions below. Note: The
cradle/transmitter on the WHP141 is not a recharging cradle, although
you may place the headset in the cradle during recharging.
Follow these steps to recharge the NiMH rechargeable batteries.
1. Make sure the ON/OFF switch (2), located on the right headphone,
is in the OFF position.
2. Connect the AC/DC main power adapter to the DC IN power
supply socket (11), located on the back of the cradle/transmitter.
3. Plug the adapter into an electrical outlet.
4. Connect the charging cable (10), located on the back of the
cradle/transmitter to the recharging input (3), located on the right
headphone. The headphones can either be placed in the
cradle/transmitter or placed next to the unit. If the headphones are
connected correctly, the charging LED indicator light on the
cradle/transmitter (8) illuminate.

CHARGE THE NEW AKUS IN ANOTHER CHARGER AND THEN USE THEM AS USUALY.
SEE THE CURENT SUPPORTED BY THE ORIGINAL GHARGER,
IF IT IS AT LEAST 100mA , IT SHOULD CHARGE YOUR NEW AKU ! BUT MAYBE THE CIRCUIT INSIDE TX DO NOT SUPPORT
AKUS BIGGER THAN 500mAh .
YOU SHOULD RESPECT THE SPECIFICATIONS GIVEN BY THE PRODUCER AND IT WILL BE OK !

Phone starts to beep after ten minutes or so then goes dead. Is there a way to change battery

I figured out the problem. My AA battery recharger was not making good contact, so although it said the batteries were recharged, this was not the case. After fixing this and getting full recharges, the problem went away.