Batterys??????????

[Edward Rupp <edwardrupp@netzero.net>]

Hello fellow EV’ers,

I have for many weeks been agonizing over what replacement batteries to
put in my car.  I have about a 40 mile round trip to work every day. 
The car as is barely makes this distance, thus dipping into the last 20%
of battery capacity.  The car is a Mazda RX-7 with 22 batteries that are
about 3 years old.  I know some people might be nervous from earlier
discussions on vehicle weight, however this car has beefed up suspension
and the brakes seem up to the job.  I believe the present batteries are
US Battery 125, marketed by Interstate battery as U2300.  Each battery
weights 68 pounds for a total pack weight of 1496 pounds.  The tough
decision is whether to get NiCads or stay with lead.  Also whether to
pay extra for AGM or stay with flooded.  My philosophy is the car is
doing great with 1500 pounds of batteries, so the replacement pack will
stay close to but not much exceed this value.  For me range is
important.  The car must be able to do 60 miles to give me a comfortable
margin.

This is what info I have so far.

U2200, sold though Interstate, actually US Battery  US2200.  Weight 63
pounds, this will allow me to add 2 more batteries for a total weight of
1512 pounds.  I plan on replacing the 40 pound accessory battery with a
small motorcycle battery thus keeping the weight about the same as the
old pack but going up to 144 volts.  The U2200 has a slightly lower
Peukert value of 1.236 over the old batteries of 1.241.  Cost $58.95
local in stock each, total pack cost $1414.80.

I could use 22 of the U2400 which have the lowest Peukert’s value of
1.166.  However I would remain at 132 volts.  Weight gets a bet high
even with the accessory bat removed at 1540 pound battery pack.

For flooded’s I’ve focus mostly on US Battery through Interstate manly
because availability is so easy and I guess the cost is lower that
Trojan and quality about the same.  Though the Trojan data indicates
slightly lower Peukert values for comparable batteries.

Next is the AGM’s  I’ve decided to focus on Hawkers manly because they
give so much more info, also data if believed indicates the Hawkers have
a much greater life cycle.  The other reason is at present Hawker makes
the biggest AGM.  The scenario here is 24 Hawker 70AH Genesis
batteries.  By far the lowest Peukert’s value of any lead battery I’ve
found at 1.06.  A bit pricer than flooded at about $152 a battery. Total
cost about $3648. Weigh 58 pounds each for a total pack weight of 1392
pounds.  Are capable of  500 cycles at 80% DOD compared to the average
of about 625 cycles for the average flooded .

Then there is the big buck battery!  Saft NiCd STM5-180.   A whopping
$595 per battery!
Total price for 24 batteries $14,280 dollars.  Wow!  However the weight
is only about 51 pounds each for a total of 1225 pounds.  They will last
just about forever, over 3000 cycles.  Plus all the other advantages of
NiCad such as no trouble with cold whether.  I focused on the STM5-180
because it uses the older charging algorithm which is less Likely to be
a problem complying with.  Also its the biggest battery and closely
matches the old packs dimensions.

So what to do?  I hate always worrying if I am going to get home and
want the most range I can get.  However am I committed enough to spend
the really big buck’s?  If I buy the flooded batteries I may not gain
much and may give up on electric cars. If I by the NiCad’s I better be
real committed to driving the car for a long time!

I love driving the car!  It amasses me how harmonious the system is,
even with 3/4 ton of lead!  The Advanced DC 9” motor is a work of art! 
Along with the modern EV components.  Such a improvement over my first
car, a 1976 Vanguard.  If only the batteries would catch-up!  The nasty
gas car wouldn’t stand a chance.

# of	Battery		$ each	$ pack	Pkrt’s#	weight	cycles

24	U2200		$58.95	$1414.8	1.236	1512	625		

22	U2400		?	?	1.166	1540 	625

24	Hawker 70AH	$152	$3648	1.06	1392	500

24	STM5-180	$595	$14,280	?	1225	+3000

Any thought’s on my possible battery solution would be appreciated.  I’d
love to drive a car in the next century that seems appropriate for the
view of a optimistic future.

Edward Rupp
RX-7 EV
Loveland Colorado
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