DC-DC booster fails with lead-acid battery source
A complete analysis of resonance is hard without datasheets and a model for each part. But the primary fault is system design with lack attention to thermal losses and cooling. It requires a fan and heatsink.  

The simple theory is the series resonance gain \$Q = \dfrac{X(f)}{R}\$ which is the reactive current gain also increases series losses \$I^2R=Pd\$ in its path such as RdsOn of the input MOSFET.  Although the battery C gives a very long time constant \$T=C*ESR\$

The MOSFET can have  a PTC tempco. and gets hotter with rising temperature leading to thermal runaway when spurious oscillations occur in the primary side switch.  Powering LED's, no problem, powering a low impedance high Q load "big problem" for a switched voltage source.

This is the nature of high frequency charging batteries is that AC currents can also be high increasing ripple currents in caps and conduction losses in MOSFETs.

Unless there is a suitable system design of impedances and peak currents and resonances, many faults may  occur.   Reducing the resonant currents comes understanding how every part's impedance contributes to the system control loop.

This will not be a thorough analysis but just a low level discussion of some prinicples.


output impedance is "transformed" to source to a lower "average" impedance by virtue of boost regulator in voltage and \$\dfrac{V_{IN}}{I_{IN}}&lt; \dfrac{V_{OUT}}{I_{OUT}}\$ for a boost regulator just as in an induction voltage transformer. Which means the low  battery impedance looks even lower to the primary switch.


The DC-DC board is on an aluminum alloy substrate of about 2 sq. in. which in free air without heatsinking will normally get hot with about 2 Watts of loss should be mounted to a large heat sink for max power transfer with thermal grease. ( details held back)

Considering the application supports up to 85W output , what are your expectations ?? for worst case efficiency into an "almost" short circuit load. ( i.e. a battery)  How hot did it get? how quikly did you react to shut it off?  


  THese are user errors not component faults.



the SLA battery has a ESR of 12V/44A or 0.25 Ohm minimum that increases as battery charge reduces or ages.  This can stretch the primary current duration when the voltage dips during cycles.  Boost regulators transform voltage up at the expense of more primary current and resonant impedances can increase energy losses.  This may leading to oscillations with a battery that has a memory effect and high ESR resulting in unstable operation. 


suggested solution: use appropriate low ESR caps that are rated for primary DC ripple current. e.g. 5Arms at the switching current frequency.  Several caps are needed to support the one on board over a range of values low-esr tantalum and plastic to span spectrum of input current.



The battery also has higher ESR than step down regulators with ultra-low ESR output caps and even some with ferrite LC post regulation output filters. 

This can cause primary boost current to resonate more. Also using the boost regulator to charge a battery with very low ESR now means an even lower impedance applied to input RdsOn switch meaning more load current.

Solution reduce current limit, add heatsink and microfan to board and add several large caps across regulator input with &lt;=10mOhm ESR.

LED loads are low ESR with eg. 47V @ 1.3A = 61W implies ESR &lt;&lt;1 Ohm unless regulated with current sink.

But Battery loads equivalent to 100k Farads have an ESR according to  voltage changes from step currents ΔV/ΔI=ESR  which is closely related to short circuit current to Voc/Isc and will be xx mΩ range.