Use of Ferrite Beads to Suppress RFI in Battery Packs

I think it's very unlikely the the battery pack is the source of the RFI, though it may be acting as an antenna. A filter on the power input to the radio amp (given a properly EMI/RFI shielded enclosure for the RF circuitry) should help.

Yes - batteries don't emit RFI. Could there be a switching power supply in the battery pack?

Ferrites will help an RFI problem if the RFI is conducted through the wires. They will not help if the RFI is emitted through the air. In this case you would need Faraday shielding of some sort.

It certainly wouldn't hurt, and experimentation with ferrite beads is fairly simple. Ferrite beads have a low value.

800MHz is not an amateur frequency, so the equipment will have been constructed and supplied commercially. It might be worth involving the supplier and the original equipment manufacturer early to see if they can give an insight into what is going on and offer advice that has been time-won from others that have had this problem, perhaps?

It would be useful to know if the vehicle engine was running, whether it's a diesel or gasoline (petrol) engine, how the RFI manifests itself in the system (symptoms), is the radio the source or victim, what other electronic equipment is in operation, is the battery part of the vehicle or is it a portable unit used in the vehicle, is the antenna mounted to the vehicle or a portable "rubber ducky" omni, or is it some kind of directional antenna i.e. TACSAT, are the symptoms noticed during the transmit or recieve mode, etc ??

Troubleshooting RFI in equipment can be very difficult and time consuming. It sounds like you are using a professional quality transmitter that requires a FCC license to operate. Like those that radio/TV stations use for remotes/news coverage and STLs. Without seeing the symptoms it would be impossible to tell what is going on. You could just be experiencing alternator noise(whiny kinda noise) via improper or insufficient grounding. The transmitter unit could be having problems and emitting spurious or inter-modulation products outside of its operating frequency. Does the unit work? Can you successfully transmit data? and receive it with the pick up receiver? You could also have a poor antenna connection that is 'leaking' RF. check all your transmission line and antenna make sure its put together properly and sealed up from elements if outside and not damaged or deformed. A deformed coax will have an impedance change where the deformation is that could cause problems. The transmission line and/or the antenna may not be a proper impedance match for the transmitting device. Make sure the cable, antenna are what the transmitter unit want to see impedance wise. 50Ω or 75Ω. Make sure the antenna is the proper antenna for the frequency being transmitted. Is your system direction or omni direction transmission pattern. Do you see any alarms or warning indicators? high VSWR or antenna fault? Does the transmitter device work from the 'bench' with out the issues you have now?

What kind of analyzer equipment do you have? spectrum analyzer or the like that you could 'see' the RF output from your transmitter. Is your transmitter calibrated recently? Or something thats been sitting around collecting dust?

Is the transmitter what produces the 45watts or is that after the antenna gain? What are the characteristics of the antenna? impedance, gain, operating frequency range?

A word of warning, 45watts doesn't seem like a lot of power but you can hurt your self messing around with the insides of the transmitter and you can also harm yourself if you place yourself close to the RF field or in the path of the beam for extended periods of time.

If you want more help. I will need specific information. Model, Make of the transmitter, the antenna, what type of cable you are using for transmission, cable length, your exact operating frequency, your meter readings on the transmitter; voltages, output power reading, program output reading, VSWR reading(simply put, this is the transmitted power that is reflected back from the antenna to the transmitter output.) any faults or alarm indications.

The first thing I would do is set this rig up on a work bench and run it into a proper antenna, safely to see if you are still having the same problems.

This may sound a bit simplistic, but checking and tightening grounds and battery connections has often cured what appeared to be RFI.