My sister popped by yesterday with a couple of items. A Dell 2408WFP monitor and a Nexus 7 tablet. The Nexus 7 has been having a history of intermittent charging. Sometimes it will charge, other times it seems to discharge – so what could be wrong? We have tried already, a different charger – most people suggest that the charger needs to be able to supply at least 2A. A look on Google shows that this is a problem faced by many Nexus 7 owners. This Nexus 7 has been so frustrating that a little while ago, they went out and bought one of those 10″ tablets that I think was on special at Aldi. I said at the time that if they don’t want the Nexus 7, they can bring it over some time and I will see what I can do with it.
First thing was to pop the back off. This is quite simple – just using a fingernail – slide it between the plastic and the metal bezel, and work your way around – the clips should easily disengage. Having longer fingernails works better. Once the back is off – you can see this large flat black item with a six wire cable coming out and plugging into a socket. The black is negative and the red is positive. I used a multimeter to connect to the socket pins and measured 0.4V – not good. The battery being a Lithium Polymer battery is a 3.7V battery. Wikipedia indicates that the first generation Nexus 7 (which this is) was powered by a 4325mAh battery. A check on eBay shows that the cheapest battery for this is a 4270mAh for just over $20 delivered.
Now, what to do with the battery – I need to “recharge.it“. Perhaps I should say to charge it, but recharge sounds better. I have a battery charger that can charge LiPo batteries. I connected it up to the battery using some small clips – the contacts are quite small. Here is a photo of the setup.
I set the capacity of the battery to be 3000mAh and the voltage to 3.7V – as being a single cell. The charger is powered by a small 12V battery. I started it and let it charge overnight.
This morning I had a look at it – it had finished charging. So I am now testing the battery. I am doing a discharge test at 0.3A – this is what the photo is showing. When the battery voltage drops to about 3.7V, the charger will automatically stop. The number at the top right hand of the display would be a number that relates to the capacity of the battery. If I charge and discharge the battery a number of times, this number should be either similar or increasing each time. The purpose of this charge, discharge test is to verify if the battery is able to retain charge. Retaining a reasonable amount of charge indicates that the battery is still good. I will come back with an update later.