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MG TD TF 1500 - Battery 'tender' vs battery 'charger'?

I did and archive search and found some info on this, but many still unanswered questions.
I just replaced my battery on my 51MGTD. The battery was only maybe 4 years old but had no juice. Now I attribute this largely to the fact that with a semi-running car, the battery probably spent a lot more time turning the engine over (draining) that it did recharging while the car was cruising.
However, I'm also wondering whether a battery "tender" could have done a better job keeping the battery alive and well, compared to my 30 year old Sears battery charger.
I really don't know what the difference is between the two, and wonder if a "tender" would be a good investment.
Hopefully some knowledgeable electrical engineer types can offer some insight...
And even perhaps some recommendations as to which ones are the best?

Geoffrey M Baker

A battery tender provides a small charge +/- 1 amp, and does not charge the battery once it is fully charged. A battery tender will constantly monitor the battery and provide a float charge when the charge drops below 100%. A wet lead/acid battery loses one percent of its charge every day. Just sitting, disconnected it will lose 30% of a charge in a month.
A battery tender is not recommended for gel cell, or glass mat batteries (Optima). These batteries do not discharge, and are best left disconnected with a battery disconnect switch.
D. Sander


I too just replaced an eleven year old battery. It went through the normal (for us) routine of neglect and then use year after year. Toward the end it always needed a charge before I could start the car. I did not leave it on the 3 amp charger for more than 48 hours at a time. I purchased a battery tender and the old battery performed Ok for about a year but reached a point that I did not dare to shut off the car if away from the garage. I think the tender added many months of use and save a bunch of screwing around and remembering to charge the day before.

Now have a new battery on the tender and all is well so far, about 3 months. Shop around, Moss is mucho $$$ compared to other sources.


Jim Haskins 1953 TD

J. M. Haskins

"Battery chargers" usually continually charge the battery, batteries heat up when charged and that causes the water to evaporate.

"Battery tenders" charge at a lower voltage level causing less heat, plus they stop charging when the battery is fully charged and then start up agin when the battery looses some charge. (Float charger)

Battery tenders will not charge a dead battery.
Battery chargers will.

Any battery that sits for periods of none use should have a battery tender attached to get the full life from it.

Deltran Battery Tender is one of the better brands, but not sold in California or Oregon because they do not completely turn off when in stand by mode.

Optima is what I have in the TF and didn't know you shouldn't put a battery tender on it. Even I haven't before, I was thinking of hooking one up. I have 4 Deltrans hooked up to my tractors now and they do a wonderful job. PJ

Posted 02 January 2016 at 18:41:12 UK time
Optima is what I have in the TF and didn't know you shouldn't put a battery tender on it. Even I haven't before, I was thinking of hooking one up. I have 4 Deltrans hooked up to my tractors now and they do a wonderful job. PJ

I had never heard that before only they didn't need it because they don't loose their charge during storage.

I went to Optima's web site, they sell a charger maintainer and recommend you use it on your Optima battery. At over three times the cost of the other maintainers.

Sears makes a small unit that combines trickle charger and battery keeper. If clipped to a dead battery, it may take 12 - 24 hours to then switches over to "tender" mode. I've used mine for about a year and had no issues
Charles Duffy

A few years back a TC and TD in the area had batteries blow up that had been on tenders or trickle chargers. The TC battery blew up when they pulled the starter. Acid started dripping into the interior, and they had to open the battery box and stick a garden hose in it to flush . Not sure if random coincidence or common? The TC battery is enclosed, and perhaps hydrogen gas? No clue about the TD. Anyone else heard of this with a tender? George
George Butz

There's another matter to consider. If a battery is consistently prevented from charging fully, it can lead to sulfation, the build-up of nonconductive lead sulfate crystals on the plates, which are difficult to get back into solution. This is one reason why batteries die. If you keep it well charged, with a well designed tender or a smart charger, it will go a long way to preventing sulfation.

However, you need to get a good unit--one that is smart enough to cut off when the battery is up to voltage. Some cheap ones just continuously trickle-charge it. In any case, it's a good idea to use something, as our cars' old charging systems don't do a great job of keeping the battery well charged.

That said, I don't use a battery tender. Instead, I have a smart charger and recharge the TD battery weekly or thereabouts. It charges the battery at constant current until it is almost completely charged and then switches to a float-charge mode, at a constant voltage, and finally cuts off when the battery is fully charged. You can select the charge current and select a program for the particular type of battery. I think it's a great tool.
S Maas

Modern units have a desulfation cycle. Regards, tom
tm peterson

You might like to look at the CTEC MXS 5.0. They have a website: ctec dot com. It includes pretty much all the features talked of in earlier posts including desulphation.
M R Calvert

I perhaps should also have mentioned that they specifically say in their literature that they are suitable for AGM batteries (i.e. Optima).
M R Calvert

I agree with S. Maas. I have a 2.0 amp charger that also is a tender. I can charge a battery with it, or I can hook it up and let it run all winter while the car is in storage.

Since using this, I have not had to replace a battery, and the car turns over perfectly when I take it out of winter storage.

I also have a very small battery tender. I use it for the lawn mower.
Bruce TD4139 Cunha

Michael C is right about CTEC MXS 5.0 12V/5A. A great product
designed in Sweden.(made in China). Fantastic device which can be
set for motorbike batteries as well.

I have my rubber case batteries for the TFs rebuilt in Melbourne,Australia. The batteries usually last around 5 to 6 years.

Whatever tender/charger you use,I feel it always pays to ventilate
the area under your bonnet. Leave the bonnet open or at least ajar.
In particular, Y types and TCs have fairly fetid battery box areas and may need liberal ventilation to avoid explosive disappointment!!


Anyone checked out these?

NOCO Genius G3500 6V/12V 3.5A UltraSafe Smart Battery Charger

Apart from the self-congratulatory name, it appears to offer pretty much everything the CTEC models do and possibly more...
Geoffrey M Baker

Harbor Freight has them for under 10 bucks, I use them on all my cars and batteries.
TRM Maine

Just found a blog revie comparing the ctek and the noco. The ctek gets a few points over the noco but at a cost. Lots of factors, interesting review.
Geoffrey M Baker

Here's the link
Geoffrey M Baker

Harbor freight battery maintainer, WalMart automatic battery charger (3 different Amp ranges) that tapers the charge down as it charges. It also has a de-sulfur cycle you can run on a battery (they recommend several times) that takes around 24 hours each cycle.

I used the de-sulfur cycle (about 5 times) on a big battery that never got used much over its 10 year life in a certain car. It would not hold a charge long. Did the de-sulpher thing and now it works just fine.
N Tesla

This thread was discussed between 02/01/2016 and 04/01/2016

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