Haier HG-9041 Tablet Fix / Repair

you should help out @mikibell . she is in the same situation with the same tablet

I think some charging circuits can read the low voltage as an error and will not apply power to the battery if everything checks out ok. I’ve seen camcorders do the same thing. Good experimenting!

This is a slippery slope. First a battery, then Linux, then you get a Raspberry Pi, then you take over the world.

Recommendation: if you do this, place it on a sidewalk (non-rainy night required here) when you charge it overnight. Likely, you couldn’t put an initial charge on it and the protection circuit engaged, refusing to charge the battery. As you mentioned, deep discharge can damage a lithium battery; sometimes this means it can cause a fire if you try to charge it. This is less often true for Lithium Polymer batteries (most likely what the tablet uses) than Lithium Ion, but it’s still good to be careful and safe. Fire bad. Incidentally, I did something similar with a DOA $3 bluetooth keyboard.

The one I got in a fuku (or was it a fuko?) works fine, except for Wifi… even with it right next to my router, it barely gets anything… I checked it and it isn’t a bad connection to the antenna (I desoldered it and then reattached it). The I got bored and forgot about it.

Hey guys! I’m an electronics nerd, and you, unfortuanately, have piqued my intrest! Roll the hour long explanation!

So these lithium ion batteries are different from the lithium polymer batteries(used in rc cars and drones) in that the electrolyte is less… caustic and flamible. dont get me wrong, theyre still dangerous but its not such a violent reaction when the lithium touches the air. More of an angry, grumpy reaction. I would (as a safety precaution) assume that the li-ion hates you personally and will burn your house down the first chance it gets.

Every lithium cell should have a protection circuit. The one exception I can think of is the r/c drones or planes, but we wont go into that here. An adequate protection circuit will provide protection against 3 main types of battery abuse. Over current, over voltage and under voltage. Theoretically you should protect against overheating the battery also, but that is not as critical with li-ion batteries. Over current - drawing too much power from the battery - causes too much heat to be generated and that heat can damage the capacity of the battery, or lead to a rupture in extreme cases(worst case scenario). Over voltage - anything over ~4.2 volts damages the energy capacity and lifespan (# of charge cycles). If the protection circuit senses over 4.2 volts per cell it will flip a switch and disconnect the battery in an attempt to prevent damage. This over voltage condition should be rare as the charger for these batteries watch their voltage like a hawk. Sustained over voltage can lead to the electrolyte “boiling”, and the case rupturing, which is very bad. Under voltage - The battery is empty, and your still using it… Until the protection circuit notices ~2.6 volts across a cell and flips the switch, disconnecting the battery and prevents it from damaging itself. This one is really important to get the maxium number of charge cycles out of the battery. Set this too low and the li-ions are being damaged the entire time they are fully depleted. Once this under voltage protection is tripped, it wont be disabled until an external voltage is applied across the cell, which is half your problem. On to the other half.

Li-po batteries are mainly used in applications where the battery needs to dump all of its power in a very short amount of time. While this sounds awesome, they achieve this increased output by using an extremely volatile electrolyte. You do NOT want this in your phone, as it is in your pocket or next to you while your sleeping 99% of the time. Say hello to li-ion battery chemistry! Its li-po’s slower, but less angry cousin! Interestingly enough, the operating voltages are practically identical and the chargers for li-poly batteries can be used on li-ion batteries. In a lot of cases, thats exactly what happens.

If you were a li-po charger, and someone plugged a battery into you and told you to charge it, would you? Personally, knowing the battery is full of this volatile liquid, I would like to inspect this battery before I start dumping power into it, as it has the very real posibility of lighting on fire if its damaged. And thats exactly what is happening. All the chargers worth the components theyre made of will check the internal resistance of each cell before applying power. If a cell is out if spec, no charging happens and the charger says no! This is a very important safety precaution, and combined with the excelent chineese q/a and engineering, the other half of your problem.

So the batteries are draining, tripping the under voltage protection, effectively disconnecting the battery. So when you plug it in, the charging circuit boots up and checks the internal resistance of the battery. Seeing as the protection curcuit already disconected the battery, theres no battery for the charging circuit to measure, and no battery means an out of spec internal resistance measurement, and no charging occurs.

You have found a way around this. Manually reset the under voltage protection by applying an external voltage, then charge the battery. Keep in mind when you do this, you are causing a (probably negligable) small amount of damage to the battery. The first stage of charging is supposed to be current limited, but its fine if its just to reset it.

If your trying to franken-battery this thing, im down to help any way I can. I have an old asus TF-101 that needs the same treatment. You can find these batteries called 18650s on teh interwebs, the ones without tabs (look like a regular AA but bigger, ie a nipple on one end and a flat side on the other) are relatively cheap, include a protection circuit inside each battery, and you can easily buy chargers and cases for them. Beware though, you wont get more than 2500mah (2.5ah) out of each battery, regardless of what the seller says, or is printed on the label. I would also purchace ones that cost 10% more than the bottom of the barrel.

Another thing to consider is the arrangement of the cells in the battery pack. Each lithium cell, li-ion and li-po, have an operating range of about 2.6 to 4.2 volts. If the listed voltage on the pack is a multiple of the previously stated range, there are at least 2 cells in series, which necesitates the use of a more complex charger. This is called balancing the cells, which is ensuring each cell in the pack is charged fully. If you have a lithium battery pack with 2 cells in series, you will see 3 wires coming out, one for the positive on battery 1, one for the negative on battery 2, and one for the positive on battery 2 and the negative on battery 1.

@awk is right to use a current limiting resistor to trickle energy into the battery when hes resetting the under voltage protection. The main difference here is if he pops his li-po’s case he has a caustic, toxic liquid that violently reacts with oxygen, now exposed to oxygen. The best part is after you put the fire out, it will start again if there are enough unreacted chemicals left.