Lithium Batteries in Handheld VHF Sets

[Dockhead]

I have just bought a couple of handheld VFH radios -- a Standard Horizon HX851 and an HX471S.

Although communications between the dinghy and mother ship, and between ship and shore, are mostly done with mobile telephones these days, it still seems to me like good practice to have some other means of communications.

Besides that, the HX851 seems to me like an essential thing to have in the grab bag in case of, God forbid, abandoning ship. The HX851 has a GPS and will do DSC. Seems to me like what you would desperately want if you found yourself in your liferaft.

For that last purpose, I bought a battery tray and a bunch of long-life lithium batteries to keep in the grab bag. The AAA lithium batteries have a capacity of 1200mAh each, so a whopping 6000mAh for the tray of five of them. The standard rechargeable Li-ion battery has only 1150mAh, so I would have thought that using the battery tray, the batteries would last for days, compared to 8 hours or so with the standard rechargeable battery.

I was quite surprised to read in the HX851 manual (http://www.standardhorizon.com/downl...pplication/pdf) that when using the battery tray, high power transmission (6 watts) is disabled (!), and that battery life will be "dramatically shortened", compared to using the standard rechargeable battery.

This does not make any sense to me whatsoever. Does anyone understand what this means?

[FloatyThing]

It probably has to do with current draw. The lithium Batts may have more capacity when being drawn from at low current, but at high current they die quickly. The rechargeable that came with your radio can withstand high current draw for longer periods of time.

[Dockhead]

Originally Posted by FloatyThing

It probably has to do with current draw. The lithium Batts may have more capacity when being drawn from at low current, but at high current they die quickly. The rechargeable that came with your radio can withstand high current draw for longer periods of time.

It's my understanding that alkaline batteries die quickly under high current loads, and don't reach their rated capacity.

But lithium batteries are supposed to be vastly better in that regard. See: http://data.energizer.com/PDFs/lithiuml91l92_appman.pdf

Has anyone used them in VHF radios? Is the life really "drastically shorter" than the standard Li-ion battery? Or does that note in the manual refer only to alkaline batteries?

[SoonerSailor]

When you put cells in series, you add their voltages not their current capacity.

The tray of lithium AAA cells will probably have a similar life to the Li-ion pack in normal use, and they will perform much better than alkaline cells. Of course, you can't recharge the lithium AAA cells, but they are good for backup and long term storage purposes.

[Dockhead]

Originally Posted by SoonerSailor

When you put cells in series, you add their voltages not their current capacity.

The tray of lithium AAA cells will probably have a similar life to the Li-ion pack in normal use, and they will perform much better than alkaline cells. Of course, you can't recharge the lithium AAA cells, but they are good for backup and long term storage purposes.

Hah, of course you're right! Duh . . .

Yes, the whole point is to have a bag of batteries -- maybe in a sealed, dessicated container -- in the grab bag so that the VHF can be used in the liferaft, where obvious there is no way to recharge the regular battery.

Has anyone tried lithium batteries in a handhelf VHF? I guess I will have to sacrifice a set and do a trial. I'll post the result for the benefit of anyone else who is using this setup. I would think it is a fairly standard grab bag setup -- isn't it?

[hellosailor]

"The AAA lithium batteries have a capacity of 1200mAh each, so a whopping 6000mAh for the tray of five of them."
You've done the math wrong. Five AAA cells at 1.5V each will be used in series, for a combined battery voltage of 7.5V but the amperage still remains 1200mA.
If you stuck the cells in parallel, they would produce a battery with 1.5V at 6000mA.
You get one or the other, not both. (A "battery" being a collection of cells, and the only batteries we really buy at the drugstore are 9V "transistor" with six AAAA cells inside, or 6V "lantern" with four "F" or "D" cells inside. Supposed to be F cells, but the cheap ones cheat you and use D cells.)

I have limited liking for AAA cells, they just don't have enough capacity to do much real work at anything, no matter how good they are.

If you call SH, their tech support are outstanding folks. Odds are they'll tell you that they disable the high power when the disposable battery tray is used, because most folks don't use lithium cells in it. They'll be honest about your best options and I'll bet a 12VDC recharging cord is one of them.

[SoonerSailor]

Lithium cells have a lower internal resistance than alkaline cells so can provide higher currents with less voltage sag - that is what they are made for. In low current drain applucations they do not have as large an advantage over alkaline cells, though they should be less likely to leak in long term storage. Your lithium AAA cells should do just fine in your VHF.

[capecuddy]

What I did was buy a replacement lithium-ion battery for the HX-851....forget the aa battery thingie. Just get the official battery....think I paid around 60 bucks and West Marine got it for me. Keep one in the charger and one on the radio.

The HX-851 is simply amazing. It also is an awesome checkout tool with your fixed mobile VHF/DSC radio since you can check out all functionality and chartplotter integration by sending the appropriate DSC requests from the handheld to the fixed unit. Then you do radio checks by doing DSC test to the USCG MMSI near you or the national CG coastal station MMSI that works anywhere.

I never do voice or ARC radio checks anymore.

[SoonerSailor]

The main problem with a Li-ion pack as backup is that it will deteriorate over time even without use, particularly if stored in the fully charged or discharged state. Typical lifetimes are given as 3 years, but i don't know what capacity endpoint is used for that number. If stored fully charged in a tropical environment, it may be even less.

Lithium primary cells (like Energizer Lithium AAA cells) have a significantly longer shelf life than Li-ion, and can be easily replaced at will.

[capecuddy]

Rotate the A and B battery.

[SoonerSailor]

Originally Posted by capecuddy

Rotate the A and B battery.

That may not help. Cycling Li-ion cells also reduces their life. The best way to prolong the life of a Li-ion cell is to store it at half charge in a cool, dry place.