9v Li-Ion batteries for Radio Mics??
 

Hi Guys

I found some Li-Ion 9 volt PP3 style rechargeable batteries that are designed for use in equipment that take normal alkaline 9 v packs... these are supposed to be a lot better than using Ni-Mh cells and they have a high capacity 500mah and hold their charge for up to 3 years. Ni-Mh are typically just 300mah!!

I spend a fortune on 9v batteries each month as my mics are in daily use up to 3 hours a day ...!!!

Has anyone used these before?? After charge they register 8.57 volts on my digital voltmeter so they won't damage any wireless gear and they certainly might save a few bucks too!!!

Any comments/advice is welcome and I wonder if anyone knows what a rechargeable Ni-Mh 9v battery reads when it is full???

Chris

Re: 9v Li-Ion batteries for Radio Mics??
 

That is the big issue. Various chemistries have different voltages, and I don't recall that ANY of them are a full 9V when charged. So even if everything else is great, they always appear to be partially depleted even when topped-off. Some transmitters won't even operate on some of those battery types.

Re: 9v Li-Ion batteries for Radio Mics??
 

Here's some general voltage info.

Assuming the cell itself is in good condition, it depends somewhat on the charger. From my experience, different chargers stop at slightly different voltages. However, in general, a NiCd or NiMH cell will top off at around 1.3v. That voltage will drop down quite quickly to around 1.25-1.20 volts, then gradually taper down from there.

By comparison, a fresh alkaline cell is 1.56v.

A conventional "9 volt" alkaline battery has six cells, for a total of 9.36 volts when fresh.

If the NiCd or NiMH "9 volt" battery also has six cells, it will start at around 7.8 volts! Yes, that could certainly be a problem if the equipment is designed for alkaline batteries only.

If someone makes a "9 volt" battery with seven cells, it would start at around 9.1 volts, which would be wonderful. But can you fit seven cells in a "9 volt" size physical package? I don't know.

Sadly, I must conclude by stating that I don't use anything with the "9 volt" size battery, so I have no experience with specific "9 volt" size rechargeable batteries from different manufacturers. Hopefully someone with a digital voltmeter will chime in with specifics about different brands.

Re: 9v Li-Ion batteries for Radio Mics??
 

Thanks Guys!!

Leaving them overnight resulted in the packs dropping down to 8.45 volts so it seems that these have 7 cells in them as 8.45/7 = 1.207 which is close to nominal but as already mentioned some gear might need the full voltage that an alkaline gives....I worked over my alkalines yesterday in the one mic pack and they are sitting at 8.52 in the transmitter pack and 8.15 in the receiver pack so if the mics can work at that level the Li-Ion batteries should be OK!!

Thanks for the input

Chris

Re: 9v Li-Ion batteries for Radio Mics??
 

Chris:

Remember, the voltages I gave were for NiCd and NiMH. Li-Ion is a more complex matter. There are several different Li-Ion chemistries, with different voltages! And you need a special Li-Ion charger... it's not safe to use a common NiCd or NiMH charger!

You can find a lot of theory online... Wikipedia, of course, is a starting point.

Typical Li-Ion "nominal" voltage is around 3.6v to 3.7v per cell, with the charger's voltage around 4.2v. Because of all the variations in electrodes, chemistry, etc., making predictions and guesses about the innards of a multi-cell battery is not nearly as simple as it would be with NiCd or NiMH cells.

Bottom line: if you really want to know what's inside those "9 volt" batteries, their typical operating voltage, etc., you'd almost need to contact the manufacturer about that specific battery type.

Re: 9v Li-Ion batteries for Radio Mics??
 

I've been using these 9v rechargeables for many years with my Lectrosonics mics, they have never failed me.
http://www.bhphotovideo.com/c/product/627506-REG/iPower_IP9V520_9V_Li_Polymer_520mAh_Battery.html

Re: 9v Li-Ion batteries for Radio Mics??
 

+1 for iPower 9v Li Polymer.

Re: 9v Li-Ion batteries for Radio Mics??
 

Thanks Guys

The Lipo batteries are good...they are a big hit with the Radio Control people too!! I had some 11v ones but I didn't know you could get a 9v until now.

At full charge the Li-Ion reads 8.45 volts and after two 2 hour shoots it's sitting at 8.1 now but still seems to power the mics perfectly...I probably use them on a daily basis for 2 x 2 hour shoots so they seenm to last fine. I bought two batteries and they came as a combo pack with the manufacturers li-ion smart charger so there is no charging issues at all.

I see B&H spec the Lipo battery just at 9v ...what is the real nominal voltage when fully charged???
They might be a better bet??

Chris

Re: 9v Li-Ion batteries for Radio Mics??
 

I think you will find the voltage is too low and your equipment will stop working very quickly as it will reach the end-point working voltage of the equipment very quickly.

I know of old Sennheiser transmitters that would work for 5 hours plus on a normal alkaline PP3 work for less than an hour on a rechargeable.

I have heard, though, of 9V rechargeable PP3s that have an extra cell and a higher starting voltage - and I have heard that some people have had success with these batteries.

Re: 9v Li-Ion batteries for Radio Mics??
 

Hi John

I'm actually puzzled as the batteries definately measure 8.5 at charge and then 8.4 the day after. I use then for the day ..probably on and off for 2 hours run time and they drop to a tad over 8 volts on my Azden wireless mics and the audio is still good at that stage and no indication of low voltage.

I wonder how they manage to configure 8.4 or 8.5??? Two cells would be 7.2 (like camcorder batteries) as cell blocks are 3.6v

Does anyone know what the bottom cutoff voltage on Azden wireless receivers/transmitters are?? The seem to be quite happy at just over 8 volts!!

I guess I need to check out Lipo batteries too

Chris

Re: 9v Li-Ion batteries for Radio Mics??
 

I just found a manufacturer of Lithium Polymer rechargeable "9v" and guess what??? The nominal voltage of these units is ALSO 8.4 volts not 9 volts or a bit higher so they seem to be much the same "structure" as Li-Ion when it comes to voltage???

Warren?? Have you measured your Lipo batteries once they are charged ?? It would be interesting to see if they also read around 8.4 to 8.5 !!!

Regarding my mic units, Azden specs simply say the battery can last up to 10 hours and when the sound quality drops, replace the batteries!!

Chris

Re: 9v Li-Ion batteries for Radio Mics??
 

Hi Guys

Just for interest I ran the 9v Li-Ion batteries hard yesterday with two long shoots for Realtors and when I returned back to my home office the transmitter batteries had dropped from 8.5 right down to 7.7 (they did work hard for the most of the morning) However the LED's on the transmitter and receiver were still bright green and audio was perfect!! My Azden receiver LED just goes dim and then off when the batteries die but the transmitter seems to turn red (indication of low voltage?)

It would still be interesting to know how long others have used either 9v Li-Ion or 9v Li-Po rechargeables before they are "flat" and what voltage they were whilst still being able to give a reasonable signal!!

Chris