DIYbanter - View Single Post

mike[_22_]

On 4/13/2018 4:59 PM, wrote:
On Fri, 13 Apr 2018 15:42:38 -0700, mike wrote:

I'm getting too old to pull-start my lawnmower.
I bought a used electric start, but the battery is shot.
A quality battery that actually has a specified internal
resistance is about $40. And even if I'm careful to keep it
charged over the winter, it's not likely to last more than
a couple of years. Depending on the source, it may have
been sitting on the shelf sulphating for years.

I went to Batteries+ and talked to the people.
I got lots of "consumer speak", but no actual
technical guidance. They're more interested in rotating
stock than selling me a battery with a recent manufacturing date.

The start surge current is 46 Amps, but settles to 15A or so
when cranking.

I have a bunch of old laptop batteries that I thought I'd
assemble into a starter battery. But even if I parallel
up enough cells, the protection circuit isn't likely to
tolerate that 46 amps. Then there's the charger...

There are lithium car jump starters for around the same
price as the lead acid. And that takes care of the protection
and charging and may have other uses beyond starting the
mower a few dozen times a year...looks like an option.

After some research, I realized that I don't know how they work.
Jump Starter specifications have gone the way of flashlight
brightness specifications. A typical EBAY listing has a
headline that says 20,000 mAh...but the fine print says
10,000 mAH...but it's in a package that might hold 2,000 mAH
of cells that are rated for 5% of the peak current required
to start a car.

If you sort the listings by price, you see page after page
of listings for ~$2, only to find that you get a cable for $2,
but if you select the battery, it's $89...or $2 plus $90
shipping.

I considered a cordless tool battery.
I have a 24V lithium drill battery with 6 18650 cells rated for 30A peak.
If I use 3 cells or parallel up 3x2=6 cells, I loose all the advantages
of protection and a working charger. And I'm thinking that 3-cells
may not be enough and 4 cells
in series might be a better option.

I'm seeking suggestions.
Maybe a pointer to a good value on a jump starter that may not
be crap.

* Batteries Plus is a ripoff place. DO NOT do business with them.

Walmart, Menards, and other places sell 12v garden tractor batteries for
around $20 (plus core). By one, and live with it till it dies. I've had
them last 5 or 6 years.

This thing is a 5AH battery with low volume/turnover.
They're not typically on the shelf. Even the local lawnmower place
had to order one and charge me for shipping.
Depending on where you buy it, it may have been in the distribution
chain for most of those 5 years.
It's also not as cheap as a 7AH alarm battery.

OR

Hire some kid to mow your lawn and pay them $20 every week,

OR

Go to a nursing home, where you dont have to mow, but you will pay $2000
every week for your care.

That's insightful. My trigger point for moving to an apartment is
when I can no longer take care of the yard. I plan to pull the plug
before I get to a nursing home.

OR

Screw around with all those laptop batteries, which may cause a fire and
burn down your house, costing you $200,000 (or more).

It's really more about the hobby than the $$.

Looking at these figures, I'd say the $20 battery is your best bet.