I don't understand why there is no mention of these batteries on the forum. I did a search for GBS and nothing pops up.
I bought 60 of the GBS 100AH and I have been testing them for capacity at a C/5 rate (20A). Of the 14 I have tested so far the lowest is 101.2AH and the highest is 105.4AH. They have been mentioned on EVTV and are the most different of the prismatic cells. The chemistry is listed as LiFeMnPo4 so there is probably a pinch of manganese in the mix. From a charging and discharging standpoint they are treated just like all the other LFP cells. Out of the box the voltage is 3.3042 to 3.3078 (for these 14 cells) so like the other brands where people bothered to measure out of the box they seem to be almost exactly at a 50% SOC. I have been charging them at 40A to 3.65V (stopping the charge at 2A) and discharging them at 20A to 2.7V. I basically get one per day done. I need to come up with some way to do a 1C or 2C discharge. I can already up the charge rate to 160 amps if I want to but I don't have a way to monitor the current at that level so I might take it to 80A. The discharge and charge curves are quite flat. I will post a plot later.
There are physical differences with these cells. The terminals are flat plates about an inch square and use 4 screws to hold the strap to the plate. With just 2 screws in place the straps cannot rotate and make contact where they shouldn't. The screws are stainless button caps with M4x0.7 thread and 10mm long. They come with a washer and split ring lock washer. The conductive straps used to tie the batteries together are supposed to be silver plated copper. I would call this tin plate and the quality is excellent. They have four of these straps stacked together to carry the high currents. The batteries come strapped four together with an aluminum extrusion endcap and four stainless straps. There is a carrying cord on each end. The terminals are protected with a snap on plastic cover so no connections are visible with the covers in place. The covers have break out tabs for strap access.
I bought the batteries from www.evolveelectrics.com
and since they had them in stock they showed up via Fedex ground in 2 days. To me this was worth the extra I had to pay.
Each cell also has a serial number. All the ones I have unpacked start with 110620 which is clearly a date code indicating a June 20 2011 manufacture date. There are 5 more digits after that.
The outside of the cases are ribbed but they also have little alignment pins and dimples molded into them. They sort of Lego together.
The above is the good stuff. I want to preface the rest with the fact that I am very happy with my purchase so far.
The bad stuff is the provided stainless steel button head screws look nice but are pretty soft. They have a 2.5mm socket in the head which I have stripped out trying to take the screws out (a few times). The threads are also not so good. I went to the local hardware store and bought 10 replacements and some different kinds of heads to see what I liked. The provided screws and the replacement button head screws look the best but even the replacements will strip out. I have a snapon torque meter in (in-lbs from 0 to 30). The factory screws strip from 8-12 in-lbs (usually closer to 8). The hardware store replacements will torque to 18 in-lbs a couple of times but eventually will strip out. The stainless socket heads have a 3mm socket and these will max out my torque gauge. I also tried a hex head screw which has a 7mm head. This is what I decided to change to. I also decided to switch to the Nord-Lock (wedge washers). They are kind of pricey but this is one area of the conversion I just don't want to have problems with. A high resistance contact on a battery terminal can ruin that cell. I have not determined what torque to use yet. It looks like from Nord-Lock's web site 17.5 in-lb is sort of the minimum. I've been going to 18 in-lb and I don't seem to be too close to the yield on the threads in the aluminum but the Nord-Locks aren't really locking at this point either. I expect 19 or 20 in-lb will be the point where they start to work properly. I wish the vendors would provide a maximum torque specification.
The terminal pads are not spaced equidistant from the sides and the ends of the cells. This means that a shorter terminal strap is required to connect cells end to end than side to side. This was pretty shortsighted. I would have gone out of my way to make those dimensions the same (its only off by an eighth of an inch or so). I would also have made the length and width a factor of 2 so the cells could be stacked either way. It is not that far off. The 60AH is the same length and width but shorter. This let them use the same terminal straps and the same four cell strapping system.
I am planning on 56 cells giving a nominal pack size of 17.9kwh. I will have four spares one of which I expect to do some sort of accelerated life cycle test. This will prove impractical unless I can automate the testing and do at least 8 cycles per day. I will pick out the worst four of the lot based on capacity. I will probably charge one up fully, discharge one to 2.7V and the third put back to 3.30V and store them this way to see how that affects them. Not sure how often I will test them. In saving out the worst cells I am making an assumption that the cells in the car will age faster than ones sitting in the box. Thus giving me a better balance in a couple of years when I might need to replace a cell for whatever reason.