Li-Po batteries work fine for trains… The risk and or behavior of said batteries as compared to Li-Ion is nearly identical with a PCB and or fuse in play with a Li-Po battery. Li-Po and Li-Ion cells are both comprised of essentially the same electrochemistry, Li-Po cells are without benefit of a metallic enclosure and attributes thereof… A PCB/PCM is NOT the wholly grail as many would suggest, but does provide additional protection many find favor with, preventing uninformed users from realizing derogatory results.
Generally speaking Li-Ion battery packs are provided with a PCB/PCM, that said it’s not inclusive, it’s optional. Generally speaking Li-Po battery packs are not fitted with PCB’s, yet they are available equipped with same or one can purchase a PCB and incorporate it into the battery pack same situ realized of Li-Ion batteries. In today’s world most Li-Po’s are equipped with cell balancing pigtails/features which can also be used together with PCB’s, and audible or visual voltage alarms (said alarms are the correct method to determine or anticipate when to stop running and recharge) .
The obvious difference of Li-Po and Li-Ion is form factor and whether or not the battery assembler incorporates or not a safety feature commonly described as a PCB and or PCM into their battery offerings.
Either type of Lithium technology is capable of bursting, being punctured, and thermal runaway, shorting or similar with equal results with like chemicals in play.
Mitigating failure modes is paramount; PCB/PCM’s limit current draw, over/under voltage conditions and short circuit protection. Peculiar to Li-Ion cells are metallic cylindrical enclosures and anti-explosion mechanical vents and or a PTC (mechanical thermal protection/positive temperature coefficient). These devices work similar to TMPRV or pop-offs atypical of water heaters/boilers and the like. In theory and or application the vents open at pre-determined pressure/temperature specifications, venting in a non-volatile mode.
Li-Po’s are typically encased in a flexible foil polymer pouch, without benefit of mechanical vents. The pliable polymer can and will rupture under the same circumstances realized of venting of Li-Ion cells.
Li-Po’s are widely used in cell phones, laptops, tablets, media players and many other applications we utilize on a daily basis.
The problems with fire or explosion are generally associated with improper user interaction, BUT poor quality materials and quality control are suspect in many failure modes (remember the several hundred thousand Sony Li-Ion cells catching fire in laptops debacle of years back).
I use Li-Po’s almost exclusively in my model trains without benefit of PCB/PCM’s. I utilize the correct charger and charge algorithms (most common reason for failure modes of Li-Ion and Li-Poly batteries). The charger prevents over charging, and or over discharge in the case of cell balancing (I use cell balancing chargers). A properly sized fuse offers short circuit protection. Over discharge/voltage depression considerations while on the rails is nary a problem if you don’t ignore same (common sense-ESV-audible/visual alarms).
FWIW: utilizing a battery equipped with a PCB or its CID (circuit interrupt device) to determine when the battery is discharged or ready to be recharged is detrimental to any lithium batteries extended life cycle. The two most prevalent factors that harm Lithium cells are heat and DOD (depth of discharge). Burning your batteries down to the PCM’s 2.5V per cell interrupt specification is a bad thing in the scheme of things if you expect to get the anticipated 300-500 cycles out of your batteries.
A battery with a PCB/PCM provides a layer of protection from inappropriate user interaction and or internal faults. KNOWN problem areas realized of user interaction: utilizing the CORRECT; charger, charge algorithm and current limiting device(s).
In years past many of the low budget Lithium chargers were NO more than minimally intelligent power supplies, relying wholly on the inherent attributes of a battery with a PCB/PCM to mitigate over-charging/voltage conditions.
Evolution and hysteria abounds from user interaction of Lithium cell/battery use, early on many realized problems from improper care and feeding of their lithium batteries which resulted in various failure modes. IMO for the most part were beyond the ignorance once prolific of Lithium battery care and use.
Lastly in my experience, realizing rated mAh specifications without benefit of voltage degradation twenty minutes into the 60 minute discharge interval is highly unlikely. In a perfect world a Li-Ion 2600mAh cell is supposed to provide 2.6A @ 3.6V per cell for sixty minutes, in my electronic loads realm it’s a fantasy…
Series-parallel batteries, i.e., two series wired batteries coupled in parallel to realize increased mAh capacity are commonplace, the problem with same is a SINGLE cell failure renders the battery nearly useless delegating an expensive battery to the recycle bin (there is NO question this will happen, just a matter of when).
Michael
