I have been doing exactly the same, saving for my next battery and I did consider buying a second.. From what I understand from this forum, the batteries tend to deteriorate with age regardless of whether they are used or not, so for that reason, I won’t be buying a second just yet.
My current battery has done a couple of thousand miles and there is not detectable fall in capacity or range, so I am hopeful that it will go on beyond the two year mark. I don’t know if the batteries deteriorate in a linear fashion or if they lose capacity exponentially with time / usage. If it is a linear deterioration, then things are looking good.
Hi Tom
Recent experience has given me some optimism that there will be some life beyond the 2 year mark for the Panasonic batteries, and supports the view that the deterioration is quite linear, at least through to 2 years.
My ProConnect, complete with second battery, was new in June 2008. The 2 batteries have each done about 900 miles, and each received some 60 charges.
Using a
mains energy monitor from the outset, both batteries required 330 watt hrs (to the nearest 10 watt hrs) of mains power for a full recharge during initial conditioning.
During this first year, they have been fully discharged to the BMS cutoff on a further 2 occasions in order to rebalance the cells to a full set of 5 lights (they had dropped to 4 lights) with a full rebalancing charge. I have not considered this to be a battery fault, but this view would need expert corroboration.
A full recharge at the 12 month point uses 310 watt hrs; the 6% loss equating exactly with the reduction in mileage on full assist (19T sprocket) from 26 miles new to 24.5 miles now.
Very recently, I have bought a second hand Agattu (in need of a lot of TLC) which has now been rebuilt to a high standard.
It must have been one of the earliest sold as it was described as 2 years old and this seems barely possible yet.
Its history was described as 1 year of daily city commuting (10 miles), followed by 1 year at the back of the garage during which time the battery had been charged just once !! The general state of wheels, gears, chain, brakes would corroborate the active life of at least 2500 miles. The bike was not in a fit state for a road test.
In line with the current forum thread regarding ebike & battery value, this would put the value of the battery well into the £0 band. On collection, the battery showed 5 lights for the state of charge, and only 3 lights for the condition of the cells (10 second button test).
Having completed the rebuild, I was keen to see the situation with the battery (and indeed verify that the charger was in good shape).
Ride 1
Started with cell condition on 3 lights, battery charge 5 lights, battery ridden to cut out in dribs and drabs whilst checking out the bike.
Charge 1
290 watt hrs of input, cell condition back to full 5 lights
Ride 2
23 miles around the same circuit that would have produced 24/25 miles on my ProConnect !! Final light flashing, but not fully exhausted.
Charge 2
270 watt hrs of input, cell condition 4 lights > slight disappointment
Ride 3
Same circuit, 24 miles to fully exhausted for another cell balancing charge.
Charge 3
290 watt hrs of input, cell condition 5 lights.
I have been out a futher 3 times for 20 miles or so and the cell condition has remained on 5 lights.
None of this is yet evidence that the battery has a significant future life, but for the present, it is perfectly acceptable at a loss of about 12% of the original capacity.
My previous experience suggests that the summer always brings out the best in batteries. A 2yr old battery is likely to have a summer left in it, but a younger battery can disappoint in the winter.
James
I have been putting away a few quid each week in a battery fund so that the hit isn't too painful further down the line, but the prices seem to be running away from my savings plan
