# Switching from 4V Lipos to standard 9V battery gotchas?

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#### jahall4

##### Well-Known Member
Hi All,

Im switching over to a standard 9v battery (smoke detector battery) in some of my larger rockets. Up till now I have exclusively used 4V 900 mah Lipo batteries like you can buy from Apogee and others.

Other than using a good quality snap connector are there any other gotchas that could be different from the use of the Lipos?

One that immediately comes to mind it whether it is okay test the drogue and main firing circuits with the same 9V battery you are going to use for a launch? Of course that raises the broader question of using a fresh battery for every launch.

#### watheyak

##### Barnstormer
TRF Supporter
I always used a fresh one every launch. I tested with a separate battery but that was only an issue for new rockets. And make sure you have a good way to secure the battery. Holders or zip-ties. Or zip-tied into a holder...

I was really happy to switch away from 9v batteries. I hated the form factor and in the end it was just really wasteful. Besides, they're heavy and take up lots of room.

#### Handeman

##### Well-Known Member
TRF Supporter
I use the same Duracell 9V battery for a whole season. As long as the altimeter reads a voltage at 9V or higher, I fly it. I suspect it would still work fine with a reading as low as 8.7 or so since my meter reads about 0.1 to 0.2 volts higher than the altimeter reports. But, just for safety sake I change them out when they get below 9.0V.

A couple of notes with that. I fly only Perfectflite altimeters which have the capacitor on the power input so they can ride through any possible momentary disconnects with the snap on connector to the battery. Also the capacitor helps ensure there is sufficient current to fire the matches. I also use only Duracell because they are built with welded internal connections. I lost my L1 rocket to what I believe was an internal battery connection issue. I only use the Duracell now and I change then out if they have an unusually hard impact/landing even if they still show good voltage.

Actually one of my rockets have finished it's second season, about 14 flights, on it's current battery. I will change it out, but I'm hesitant to do that because the current battery has been flight tested and proven. A new one is a large risk because it is unproven and could have internal connection issues.

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#### jahall4

##### Well-Known Member
...I change them out when they get below 9.0V
I'm like you why replace something that is proven. So how many flights do you typically get before it drops below 9V?

#### OverTheTop

##### Well-Known Member
TRF Supporter
Not all 9V batteries are built equal. Some of them are a number of smaller individual cells in series in an outer wrapper, just held together by compression forces. Under boost they can go open. I haven't seen this construction for a while though.

If I am using 9V batteries I get one more than I need and do an autopsy on one, cutting it open and checking it does not have that sort of internal construction. Once you verify that particular model number (written on the battery) is good, you should be able to purchase the same ones in the future with confidence.

Also, don't be tempted to solder onto the top terminals. The heat melts the plastic top cap and takes pressure off the connections inside the battery, increasing probability of disappointment.

#### rocket_troy

##### Well-Known Member
I'm like you why replace something that is proven. So how many flights do you typically get before it drops below 9V?
Well, (generally speaking here) you just need to be a bit careful relying solely on a voltage reading to determine the charge capacity remaining in the battery - in particular if you're measuring that voltage with no effective load. Most batteries will lose voltage as they run down in charge like carbon cell and alkaline flavours, but other types like lead acid might maintain a voltage close to nominal but increase in internal impedance as they run down. LiPos can maintain a reasonable voltage for fair portion of their drain, but they also tend to maintain a reasonably low internal resistance until they're spent IIRC?
Again, this isn't specifically related to the 9V batteries under discussion, but probably worth mentioning as a general issue with batteries.

#### jahall4

##### Well-Known Member
Well, (generally speaking here) you just need to be a bit careful relying solely on a voltage reading to determine the charge capacity remaining in the battery - in particular if you're measuring that voltage with no effective load.
Yep it is worth the mention. The StratoLogger CF (that Handeman mentioned) does have a software testing routine that appears to be repeatably testing the altimeter, suggesting it is done under load; however, that would not be the firing load for the ejection charges. I guess one could measure the amperage during the drogue and main tests which the software for the CF also supports.

#### Dave A

I use Duracell Quantum, with all my Stratologgers

#### timbucktoo

##### Well-Known Member
Staff member
TRF Supporter
Global Mod
I use Duracell Coppertop 9V, 2 flights max.

#### jahall4

##### Well-Known Member
I use Duracell Coppertop 9V, 2 flights max.
What have you seen happen after the 2nd flight?

#### Buckeye

##### Well-Known Member
TRF Supporter
Hi All,

I&#8217;m switching over to a standard 9v battery (smoke detector battery) in some of my larger rockets. Up till now I have exclusively used 4V 900 mah Lipo batteries like you can buy from Apogee and others.

Other than using a good quality snap connector are there any other gotchas that could be different from the use of the Lipos?

One that immediately comes to mind it whether it is okay test the drogue and main firing circuits with the same 9V battery you are going to use for a launch? Of course that raises the broader question of using a fresh battery for every launch.
I am still using 9V Duracells (in my big rockets) because they are simple. I still don't fully understand all the details about LiPos, like connectors, chargers ($65 or more), and circuit protection. Wire your ematches wrong, and you can fry your altimeter with LiPos (see the various threads about parallel vs. serial redundant ematches). None of these problems with 9V. Just keep it very secure, and mount it perpendicular to flight, if possible. Depends on your altimeter. I got 12 DD flights on a 9V one season. This is with a Perfectflite MAWD with big capacitor. My other alt is a MARSA, and I used the same battery for 3 flights so far. Maybe that is far as I will go. New battery per flight is not always necessary, and I find that to be wasteful. #### timbucktoo ##### Well-Known Member Staff member TRF Supporter Global Mod What have you seen happen after the 2nd flight? Nothing. Batteries are cheap. Some people use them for 4 flights, some all season. Me, after 2 flights I use new ones. Just personal preference. Last edited: #### rharshberger ##### Well-Known Member Nothing. Batteries are cheap. Some people use them for 4 flights, some all season. Me, after 2 flights I use new ones. Just personal preference. The used batteries work great for smoke detectors. #### Handeman ##### Well-Known Member TRF Supporter I'm like you why replace something that is proven. So how many flights do you typically get before it drops below 9V? I don't really keep track. It is usually 10+ or so. #### Maxitout ##### Well-Known Member I've made it a habit to replace my 9V batteries after just 1 flight. (Duracell, of course). I take the used ones and plug them into the smoke detectors, or use them as ground test batteries. I figure the cost of the rocket and electronics outweighs the cost of a$2-$3 battery. Phil L. #### jahall4 ##### Well-Known Member I've made it a habit to replace my 9V batteries after just 1 flight. (Duracell, of course). I take the used ones and plug them into the smoke detectors, or use them as ground test batteries. I figure the cost of the rocket and electronics outweighs the cost of a$2-$3 battery. Phil L. So you have never seen a new battery fail? I would think the odds of an brand new battery failing are greater than that of a proven almost new battery. #### watermelonman ##### Well-Known Member I use a mix of 9v and lipo. I keep a 1k resistor in my electronics box, stick it between the leads when volt testing a 9v for more accurate numbers. Beware believing an unloaded circuit reads a set range away from accurate, it can fluctuate a ton depending on conditions. #### blackjack2564 ##### Crazy Jim's Gone Banana's TRF Supporter So you have never seen a new battery fail? I would think the odds of an brand new battery failing are greater than that of a proven almost new battery. Yes..... I Always check new batteries with voltmeter. Over the years... 4....2 had less than 3 volts, 1 dead, 1 5 volts. All new, all had 2-3 years left from stated use date. Have also given 2 to flier's who's "new" battery was defective also. So that's 6 in 13 years. Keep in mind I order 48 batteries at a time, have 15 altimeters & been through over 400 over the years. #### manixFan ##### Not a rocket scientist I just flew 4 flights at BALLS (3 with redundant altimeters) with all LiPos, 1S for Featherweight Raven's and 2S for the Stratalogger CFs. Before that it was always a new, tested 9 volt used only once and then retired. The average money I have into a dual deploy rocket is$500+ so the idea of reusing a battery is just crazy to me. I trust a new battery that has been tested with a battery tester that applies a load during testing far more than one that has been flown before and subjected to unknown forces. Plus no way am I tracking how long a rocket has been armed on the pad and then laying out in a field beeping out the altitude, etc.

At BALLS last year I had 3 flights with redundant altimeters so my cost for 9 volts was less than $15. For that kind of money I just can't see reusing a 9 volt more than once. Folks that do have way more faith in batteries than I do. Even with my LiPos I consider the tiny 1S cells that the Ravens use to be single use. They are less than$2 each and not worth the effort to maintain. The 2S batteries are more robust so they will get several uses before they are retired. I went with LiPos to save weight and size. The biggest issue with a 9 volt is securing it and the much lower mass of the LiPos makes them much easier to keep in place.

But to each his own. What works for me may seem wasteful to someone else. I only went to LiPos after a lot of research and testing. I've never had a failure of any kind with my dual deploy rockets in 15 years and I don't want to start now.

10+ flights from the same 9 volt battery? I could never sleep at night before a launch with that kind of mileage on a battery. But I'm sure Handeman would say he couldn't sleep at night with a new, unflown battery. To each his own.

Tony