Save 3.5lbs. by making a lighter battery for your bike!

The newer LiFePO4 (LFP) cells are ideal for a motorcycle starter battery application. The cell I used can deliver plenty of burst current, up to 150 amps for a few seconds and up to 42A continuous, to start the engine and is significantly lighter and smaller than sealed lead-acid (SLA) or absorbent glass mat (AGM).

In this mini 'how to' I'll show you how I replaced my 6aH ~70 oz. battery with a 2.5aH ~13 oz pack made from parts available at Batteryspace.com. In addition, this pack is much smaller. Stock battery is a Yuasa YTZ7S, measuring 4.5" x 2.75" x 4.5". The new pack I made is 4.5" x 2.9" x 1". The width is the same so it fits nicely in the built-in battery tray. Access to the air filter is much improved too.

The cells I used are: http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=4203

There are higher capacity cells available, up to 3.4aH, but they aren't able to deliver the high max burst discharge current as the lesser 2.6aH cells.

One could make a 5.2aH pack by doubling the number of cells to eight. The arrangement would not be a simple series though, it would be a parallel/series combo...but I digress, 2.6aH is fine for my use.

The key spec is the high max discharge current. This is required to turn over the engine, especially when cold. Even though the starter fuse is only 20amp, I measured brief bursts of ~27amps during cold start (bike was cold, but ambient was ~70 deg F) of my 08 TE250.

Along with the cells I purchased battery holders, http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=3812 to support the cells and give it structure to withstand the rigors of offroad dirt riding.

I also purchased PVC shrink (4.75") to cover the whole package. http://www.batteryspace.com/index.asp?PageAction=VIEWPROD&ProdID=1188

I started by carefully inserting the cells into the holders top and bottom. Be very careful to avoid shorting these cells in particular (or any cells), they can discharge massive current very quickly!

I then temporarily zip tied the holders, and used hot glue between the cells, both sides, for support.

I used no PCB or other circuit in this pack. The motorcycle regulator controls charge voltage and current, and the cut off voltage for the pack is much lower than the voltage required to spin the starter motor. The charge profile is very similar to lead-acid. While the pack is very unlikely to explode or catch fire for any reason, be nice to it and don't excessively over charge it. Cut off charge voltage is 4.1v/cell or 16.4 for the pack. Best to keep it closer to recommended 3.65v/cell or 14.6v/pack. See cell specs: http://www.batteryspace.com/prod-specs/4203.pdf

I ordered cells with solder tabs, but knew they would not be sufficient for the current this pack would need to deliver, in retrospect I should have ordered tabless and used solder bars. I used ~9awg wire to make my own bars. They just don't look quite as nice as solder bars/bridges but serve the same purpose.

I didn't want to alter the existing cabling on the bike, so I made up leads for the pack using ~10awg wire, I doubled up to ensure it would, again, handle the current, using heavy gauge crimp-on connectors that I also soldered. This made for a flatter, more flexible lead versus a single 8awg+ wire.

I applied two layers of 4.5" PVC heat shrink wrap, added velcro and tested. Just to be safe, I secured with two zip ties. Combined with the velcro, this lightweight pack stays put.

The new battery pack saves almost 3.5lbs. of dead weight high up on the motorcycle. This is significant savings that is not easy to achieve in other ares that are up so high on the bike. Short of riding with less gasoline there is not much one can do.

I hope this 'how to' is helpful for others. The engine starts exactly as it did with the Yuasa, very quickly and easily.

Assembly and final pictures are here: http://picasaweb.google.com/bbarden/LiFePO4Battery#

Brett

Great info! I assume there are no charging isses from the bikes charging system or a normal 12V trickle charger? This is a great DIY project for me. Thanks for posting.

Would this battery type work well to run a set of handlebar mounted HID lights that are wired directly to the battery pack?

No charging issues. I've had a Optimate III for years, works great to charge or top off the LFP pack. A 'battery tender' will do fine too. There is little reason to need to keep these on a tender though, their internal resistance is low and their self-discharge is very low, <5%/month. Chargers designed for lead-acid are actually a bit gentler than chargers designed for LFP. The lead-acid charger will only get the cell to ~95%-97% capacity, but who cares, the little bit more capacity is not worth the cost of a specific LFP charger for me.

HIDs should be fine direct to the pack, this is best for the HIDs too, so they always see power and don't go on/off/on repeatedly when the engine starts/stops. I would expect running HIDs (~25W) for a couple of hours would be no problem, even if you do consume some of the packs capacity...the charging circuit should be able to supply at least 1a+.

I have a set of Trailtech 13w helmet lights, they draw 2amps combined, so the pack alone would drive them for over two hours. Great for mountain biking, light light!

Great info thanks for sharing. You need to package these for sportbikes the stock batteries last a year if you are lucky. Good work!

If you were to stall the engine several times over a period of just a few minutes and used the button each time to restart the engine, how many 'starts' can you get out of this setup before it's dead and needs recharging?

How much $ did this kit end up costing you?

TIA,
Gary

john01: At least a couple of individuals and several companies do make nice packaged units for all markets, they are just a bunch more money than the individual cells and some time with a solder gun and heat gun. I enjoy my hobbies but am very careful to not confuse them with business. It takes out all the fun. If the sport bike batteries are only lasting a year, I would look at the charging system, probably overcharging and cooking them.

BentAero: The number of starts really depends how much current your particular bike/setup is drawing during each start. Another nice characteristic of the LFP is low voltage sag, this means you can use more of the batteries' capacity before the voltage drops too low to turn over the starter/engine. Several (8-10) starts in a few minutes should not be a problem, assuming the engine fires within 1-2 revolutions. Any more than this would be starter abuse never mind the battery.

Even after the battery is too 'exhausted' to start the engine, there should still be enough voltage for the ECU (and fuel pump) allowing you it to start using the kick starter.

Sorry, almost forgot to add the cost. I paid total $60 w/tax and shipping, I also bought some extra PVC wrap cause it's useful and cheap.

I got out for a short 90 mins. ride this morning. 3.5lbs. gone feels like so much more, the bike is without question easier to tip into turns, and feels easier to balance too, the center of gravity is now lower. I'll ride a few more times but have a feeling I'll need to add one click of rebound to the shock to compensate for the lost weight.

I stopped and started the bike 10+ times total, 4-5 times in a row just to test the battery, no problem turned the engine over with the same authority as the stocker.

Cool. Nice to know the components can be purchased online. Since I'm so lazy, I skipped the do-it-yourself part, spent a bit more money and went here to have someone else assemble mine.

The battery is only about 24 hours old. One ride so far.

These cells are rated for >2000 cycles. At 2000 cycles it should have 95% of it's orginal capacity. These cycles are 100% depth of discharge, meaning it's completing depleted, in our application the cells should very rarely be fully depleted. This cell chemistry has not been around (as least not available to us) as long as their projected life...yet...time will tell.

It should last 6-7 years easily.

Great write up Brett. Very cool.

Wish i could buy a couple. Im too busy to take on another project right now.

Anyone want to make some money? I need two.

+1

very cool!

you should start making these for cafe members, im to lazy at the current moment, winter is depressing

i just emailed him this morning on which battery he recommends, his 2.5 or 5.

i'll wait for your results since we both decided the 5 would be safer, but its twice the size

nice!. my only concern is mine is an efi and will soon be running all the turn signals dual sport stuff

im going to take a gamble and order his 2.5

Don't worry, I have been running a 2.5 in a '08 TE 450 for 3-4 months and it has never let me down.

Wow...so that would be a 4 pound reduction off an already light bike...nice?!?!